1
UNIT 3 : ENERGY CHANGES AND RATES OF REACTION
Day 1 ( Pg 298 )
Definitions :
Thermochemistry –
Thermal Energy Heat
-
Temperature
-
System
-
Surroundings
-
________ Systems: One in which both matter and energy can move in and out of.
____________ Systems: One in which energy can move in or out, but matter cannot.
2
_________ System: An ideal system in which neither mass nor energy can escape, e.g., bomb calorimiter
i.
Physical
Thermochemical equations :
H2O (s) + 6.03 kJ <-------> H2O (l)
heat of fusion
H2O (l) + 40.8 kJ <-------> H2O (g) heat of vaporization
H2O (s) +
Endothermic reactions Exothermic reactions -
<-------> H2O (g) _________________________
reactions that absorb energy from the environment
reactions that release energy to the environment
the forward reactions are
reactions whereby the
higher P.E. than the
also the
considered more stable than the ______________________________
reverse reactions are
; when 1 mole of water is frozen
energy is ________________________________
would be
are at a
kJ of
3
Potential Energy Diagrams : complete the following
-
a.
ice to water
b.
steam to water
c.
steam to ice
d.
water to steam
see table pg 4. What are the typical energy values for physical changes ______________________
Heat Content or Enthalpy (pg 303)
-
is the energy stored in a substance during its formation
represented by the symbol " H "
total value of the energy at a constant pressure
Enthalpy change ( H )
-  H = Hproducts - Hreactants
H2O (s) + 6.03 kJ -------> H2O (l)
ii.
 H = + 6.03 kJ/mole
Chemical changes
- may be endothermic or exothermic
Endo :
N2(g) + O2(g) + 180.8 kJ ----> 2 NO (g)
4
H=
products and the
Exo.:
H =
products and the
kJ/mol NO : enthalpy of reactants is
are more stable
than the
2 C2H6(g) + 7 O2(g)---> 4 CO2(g) + 6 H2O +2957kJ
kJ/mol C2H6 : enthalpy of the reactants is
are more stable.
than the
Sketch P.E. diagrams below :
-
consider the reaction above to break the bonds of the reactants energy is required ; when bonds
are formed in the formation of the product energy is released. If more energy is released in
forming the bonds then is required to break the bonds the reaction is ____________________ and
the opposite is true for _________________________ reactions
Classify these reactions as endo or exo :
-
1.
2H2(g) + O2(g) -----> 2 H2O + 571 KJ _____________________________
2.
Mg(s) + 1/2 O2(g) ---> MgO + light
_____________________________
3.
A + B - energy ---> AB
_____________________________
4.
Ag2O + energy -----> 2 Ag(s) + 1/2O2(g) ___________________________
5.
When calcium is added to water the temp. changes from 22oC to 26oC. ____
6.
As solid sodium nitrate dissolves in water at 25oC the temp. changes to 22oC _____
for chemical changes the energy range is ___________________________________
5
iii.
Nuclear Changes ( pg 341 – 346 )
a.
Atomic fusion 2
1H
-
+
3
1H
2 nuclei are welded together to form a
slightly
total mass
---------->
4
2He
+
1
on
nucleus of
+ 1.7 x 109kJ
chief source of radiant energy emitted by the sun is the conversion of hydrogen to helium , a temp. of
20 million degrees is needed to trigger the reaction :
4
b.
1
1H
---------->
Atomic Fission -
4
2He
+ 2
0
1e
------> positron emission
atomic nucleus is made to split into 2
smaller fragments having roughly
equal masses .
235
92U
-
-
+
1
0n
------> 14156 ____________+ 9236 ________ + 3 10 ___+ 2x1010kJ
the neutrons produced in the above reaction collide with other U - 235 nuclei causing them to split
and produce even more neutrons , thus a chain reaction occurs and if a large enough mass of
Uranium is present ( the critical mass ) this chain reaction gets out of control; the enormous amount
of heat produced results in the fireball that is observed when an atomic bomb explodes.
typical energy changes are ___________________________________
6
Day 2 :
Energy Changes in Reactions : Use the factor label method or unit analysis
Ex.1
Calculate the amount of energy required to evaporate 2.00g of water :
H2O (l) + 40.8 kJ ------> H2O (g)
Heat required =
40.8 kJ
1.0 mol H2O
-------------- x -------------- x
1 mole H2O(l)
18.0 g H2O
2.00 g H2O (l)
=
Alternate solution : Q = heat required = H x n (# of moles) = H x m/M
Ex.2
Calculate the heat gained by the surroundings when 1.00 g of steam condenses:
Heat gained =
Q=
= _____________ kJ
kJ
7
Ex.3
Calculate the heat gained by the surroundings when 1.00g of hydrogen burns:
2 H2 + 1 O2 ----> 2 H2O + 572 kJ
Heat gained =
=
kJ
Q=
Ex.4
Calculate the heat gained by the surroundings when 1.00 g of U -235 undergoes fission :
235
92U
+
1
0n
----->
141
56Ba
+
92
36Kr
+3
1
0n
+ 1.9 x 1010 kJ
Heat gained =
=
kJ
Q=
Ex.5
Consider the reaction : C + O2 ----> CO2 + 393.5 kJ
a.
What quantity of heat is released when 24.0 g of carbon is completely burned?
Heat released =
=
kJ
Q=
b.
What mass of carbon would have to be burned to release 39.3 kJ to the surroundings ?
mass of carbon =
= ________g of C
or m = Q x M
------H
Practice pg 308 ( 1 ), pg 319 (2) pg 320 Practice ( 4 ,5 ); pg 320 ( 1,2 )
8
Thermochemical Equations and Stoichiometry
Reinforce your understanding of the stoichiometry of thermochemical equations.
Answer the questions below in the spaces provided.
1. Consider the following thermochemical equation:
ΔH = –878.2 kJ
2ZnS(s) + 3O2(g)  2ZnO(s) + 2SO2(g)
(a)
How much heat is released when 3.0 mol ZnS(s) reacts in excess oxygen?
(b)
How much heat is released when 2.3  10–2 mol ZnS(s) reacts in excess oxygen?
(c)
What is the enthalpy change when 223.9 g ZnS(s) reacts in excess oxygen?
(d)
What is the enthalpy change when 0.96 g ZnO(s) is produced?
2. Slaked lime (Ca(OH)2(s)) is produced when lime (calcium oxide, CaO(s)) reacts with liquid water. 65.2 kJ of
heat is released for each mol of Ca(OH)2 that is produced.
(a)
Write a thermochemical equation for the reaction.
(b)
What is the enthalpy change when 523.3 kg of lime reacts with excess water?
3. The following reaction represents the complete combustion of hexane, C6H14(l), at SATP.
C6H14(l) +
19
O2(g)  6CO2(g) + 7H2O(l)
2
ΔH = –4163 kJ
(a) If 0.537 mol of carbon dioxide is produced in the reaction represented by the equation above, how
much heat is released by the reaction?
(b) If 25.0 kg of hexane is burned in sufficient oxygen, how much heat will be released?
(c) What mass of hexane is required to produce 1.0  105 kJ of heat by complete combustion?
9
Calorimetry - science of measuring heat; based on temperature changes.(pg 300).See assumptions pg 309
Calorimeter -devise used to measure temp. changes List Assumptions at the side.
Define the terms : ( pg. 301 )
1.
Heat Capacity ( C )
2.
Specific Heat Capacity ( c )
For exothermic reactions
Heat released in a chemical reaction = Heat absorbed by the Calorimeter and Contents
Qsubstance
= - [Qsolution] For a coffee cup calorimeter
Qsubstance = -[Qcalorimeter + Qwater] For a bomb calorimeter
Qsubstance = Heat released = ΔH x n
Heat absorbed = Q = mct
or Q = Ct
n = # of moles
Remember for solutions : n = C X V and for solids : n = m/M
ΔH x n =
-[mct ]
or
For endothermic reactions
-[Qsubstance]
= [Qsolution] For a coffee cup calorimeter
-[Qsubstance] = [Qcalorimeter + Qwater] For a bomb calorimeter
( mass / molar mass )
ΔH x n = -[ Ct]
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Ex. 1
50.0 mL of 1.0 moL/L HCl at 25oC is mixed with 50.0 mL of 1.0 moL/L NaOH also at 25oC. After the
reactants are mixed by stirring in a coffee cup calorimeter, temp. rose to 31.9oC. Calculate the heat
of the reaction per mole of H+.
molecular equation : NaOH ( aq ) + HCl ( aq ) ----->
ionic equation :
+
+
net ionic equation :
+
+
Heat lost
= Heat gained
Qsubstance
= - Qsollution
ΔH x n
= - ( mct )
+
-->
_______________
+
+ __________
-------> ________________________
ΔH x C x V = - ( mct )
ΔH
Ex.2
=
A 2.56 g sample of anthracene ( C14H10 ) was burned in a iron calorimeter
( c= 0.452 kJ/kg x oC ) having a mass of 0.948 kg. The calorimeter was immersed in 1.450 kg of water (
c = 4.18 kJ/Kg x oC ). The initial temp. of the system was 21.8 and the final temp. was 37.6oC. Calculate
the heat of combustion of anthracene.
Heat lost
Qsubstance
ΔH x n
= Heat gained
= -[ Qcalorimeter + Qw]
= -[( mcalorimete ccalorimetet)+ (mwcwt)
ΔH x m/M = -[( mcalorimete ccalorimetet)+ (mwcwt)
ΔH =
Ex. 3
1.435 g of naphthalene (C10H8) is burned in a bomb calorimeter. There is exactly 2000.0 g of water
surrounding the naphthalene. The intial temperature of the water is 20.17 oC. The heat capacity of
the bomb calorimeter is 1.80 kJ/ oC. The heat of combustion of naphthalene is –5.15  103 kJ/mol.
11
Calculate the final temperature.
12
Problem Sheet - Heat of Reaction and Chemical Equations/ Calorimetry
1.
Hydrazine, N2H4 (l) is used in rocket fuel. The thermochemical equation of the combustion of hydrazine is:
N2H4 (l) + O2 (g) ---------> N2 (g) + 2H2O (l) + 622.4 kJ
What quantity of heat is liberated by the combustion of 1.00g of N2H4 (l )? [ 19 kJ ]
2.
Given the equation:
2NaN3 (s) + 42.7 kJ -------> 2Na (s)
+
3N2 (g)
What amount of heat is needed to prepare 0.325 kg of N2? [ 165 kJ ]
3.
Given the equation:
2NH3 (g) + 3N2O (g) -------> 4N2 (g)
+
3H2O (l) + 1010 kJ
a)
What quantity of heat is liberated by the reaction of 45.0 g of N2O (g) with excess NH3 (g)?
b)
What quantity of heat is liberated by the reaction that produces 45.0 g of N2 (g)? [ 406 kJ ]
c)
What mass of NH3 (g) in excess N2O (g) is needed to produce 6000 kJ of heat? [ 202 g ]
[ 344 kJ ]
4.
A 3.5g sample of quinone, C6H4O2, was burned in excess oxygen in a calorimeter. The calorimeter
contained 1.2 kg of water and had a heat capacity of 3.34 kJ/C. The temperature of the calorimeter
and its contents increased from 19.0 C to 28.0 C. What quantity of heat would be liberated by the
combustion of 1.00 mol of quinone? [- 2320 kJ ]
5.
The combustion of 1.00 mol of glucose, C6H12O6, liberates 2.28 x 103 kJ of heat. If 2.0g of glucose is
burned in a calorimeter containing 1.0kg of water and the temperature of the assembly increases from
21.0 C to 24.5 C, what is the heat capacity of the calorimeter? [ 3.06 kJ/ C ]
6.
The combustion of 1.00 mol of sucrose, C12H22O11, liberates 5.56 x 103 kJ of heat. A calorimeter that has
a heat capacity of 1.75 kJ/C contains 0.500 kg of water. How many grams of sucrose should be burned
to raise the temperature of the calorimeter and its contents from 23.5 C to 28.0 C?
[ 1.06 g ]
7.
A 2.56g sample of anthracene, C4H10, was burned in a calorimeter with a heat capacity of 0.428 kJ/C.
The calorimeter was immersed in 1500 g of water. The initial temperature of the assembly was 22.4 C
and the final temperature was 38.2C. Calculate the heat of combustion of 1.00 mol of anthracene.
[- 2397 kJ ]
** specific heat capacity of water is 4.18 J/gC or 4.18 kJ/kgC
Practice pg. 310 (4),pg. 311 (10) pg 312 (2,5) pg 320 (4 )
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Day 3 :
Law of Heat Summation (Hess's Law) pg 323
For any reaction that can be written in steps, the standard heat of reaction is the same as the sum
of the standard heats of reactions for the steps.
One of the most useful applications of Hess's law is the calculation of the value of Ho for a reaction whose Ho is
unknown or cannot be measured. Hess's law says that we can add thermochemical equations, including their
values of Ho, to obtain some desired thermochemical equation and its Ho.
Example Problem: Consider the following thermochemical equations:
C(s) + 1/2O2(g) ------> CO(g)
∆ Ho = -110.5 kJ
CO(g) + 1/2O2(g) ------> CO2(g)
∆ Ho = -283.0 kJ
Use them to find theHo in kilojoules for the reaction.
C(s) + O2(g) ------> CO2(g)
Solution : Equation 1 has C as a reactant so leave as is ; equation 2 has CO 2 as the product so leave as is
i.
ii
C(s) + 1/2O2(g) ------> CO(g)
∆ Ho = -110.5 kJ
CO(g) + 1/2O2(g) ------>CO2(g)
∆ Ho = -283.0 kJ
________________________________________________
C(s) + 1/2O2(g) + CO(g) + 1/2O2(g) ------> CO(g) + CO2(g)
Cancel what is common on both sides and up the individual ∆H values
________________________________________________________________________
Example Problem #2
Carbon monoxide is often used in metallurgy to remove oxygen from metal oxides and thereby give the free
metal. The thermochemical equation for the reaction of CO with iron(III) oxide, Fe2O3, is
Ho = -26.74 kJ
Fe2O3(s) + 3 CO(g) ------> 2 Fe(s) + 3 CO2 (g)
Use this equation and the equation for the combustion of CO
CO(g) + 1/2O2(g) ------> CO2(g)
Ho = -283.0 kJ
to calculate the value of Ho for the reaction
2 Fe(s) + 3/2O2 (g) -----> Fe2O3
14
Consider diagrams : Show how equations and individual heats of reactions can be added.
15
Hess’s Law Problems
1. Calculate H for the hydrogenation of ethene to ethane:C2H4(g) + H2(g)---> C2H6(g)
using the following data:
Reaction
H (kJ)
2H2(g) + O2(g) 2H2O(l)
-571.6
C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(l)
-1411
2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(l) -3120
2. Calculate H for the formation of nitrous acid:
HCl(g) + NaNO2(s)  HNO2(l) + NaCl(s)
using the following data:
Reaction
H(kJ)
2NaCl(s) + H2O(l)  2HCl(g) + Na2O(s)
507
NO(g) + NO2(g) + Na2O(s)  2NaNO2(s) -427
NO(g) + NO2(g) N2O(g) + O2(g)
-43
2HNO2(l)  N2O(g) + O2(g) + H2O(l)
34
3. What is the enthalpy change for the formation of one mole of butane (C4 H10) gas from its elements?
The reaction is:
4C
(s)
+ 5H2(g) C4H10(g) H ° = ?
The following known equations,determined by calorimetry,are provided:
(1) C4H10(g) + 13/2 O2(g)  4 CO2(g) + 5 H2O(g) H °1 = - 2657.4 kJ
(2) C(s) + O 2(g)  CO2(g) H °2 = - 393.5 kJ
(3) 2 H2(g) + O 2(g)  2H2O(g) H °3 = - 483.6 kJ
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HESS’S LAW PROBLEMS
1. Find the H for the reaction: SO2(g) + ½ O2(g) ---------> SO3(g)
[-99 kJ]
given the following equations:
S(S) + O2(g) ---------> SO2(g)
H= -295 KJ
S(s)
H= -394 KJ
+ 3/2 O2(g) --------> SO3(g)
2. Find the H for NH3(g) + 7/4 O2 (g) --------> NO2(g) + 3/2 H2O(g)
given:
½ N2(g)
½ N2(g)
H2(g)
H = -46.15KJ
+ 3/2 H2(g) ------------> NH3(g)
+
O2(g)
--------------> NO2(g)
+ ½ O2(g)
-------------->H2O(g)
3. Find theH for C(s) + H2O(g) -------> CO(g) + H2(g)
given:
C(s)
+
CO(g)
+ ½ O2(g) -------------> CO2(g)
H2(g)
O2(g)
+ ½ O2(g)
[-282.4 kJ]
H = +33.81KJ
H= -241.6 KJ
[132 kJ]
H= -393 KJ
-------------> CO2(g)
H= -283 KJ
H= -242 KJ
-------------> H2O(g)
4. Find the heat of combustion for C2H6 from the below equations: [-1557 kJ]
C2H4
+
3O2
C2H4
+
H2
H2
+
------------> 2CO2
------------>
½ O2 ------------>
C2H6
H2O
+
2H2O
H= -1409 KJ
H= -137 KJ
H= -285 KJ
17
5. Is the following reaction exo or endothermic?
3 C2H2(g) ----------> C6H6(l)
given:
2CO2(g) + H2O(l)
C6H6(l)
--------->
[-630 kJ]
C2H2(g)
+ 5/2 O2(g)
+ 15/2 O2(g) --------> 6CO2(g) + 3H2O(l)
H= 1299 KJ
H= -3267 KJ
6. Calculate the heat of reaction for the following reaction :
N2H4(l) + 2 H2O2 (l) ----> N2 (g) + 4 H2O (g)
Given the reactions :
N2H4 (l) + 3 O2 (g) ------> 2 NO2 (g) + 2 H2O (g)
H = -466 kJ/moL
H2O (l) + 1/2 O2 (g) ----> H2O2 (l)
H = + 98 kJ/moL
1/2 N2(g) + O2(g) -----> NO2 (g)
H2O (l) -----> H2O (g)
Practice pg 326 ( 1-3 ) Pg 329 (4)Pg 330 ( 2 )
Day 4
Lab : Hess’s Law pg 351
H = + 34 kJ/moL
H = + 44 kJ/moL
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Day 5 :
Method II : Calculating heats of reactions using heats of formations ( See pg 798 )
Heat of Reaction =
Sum of the heats of formation of the products minus the sum the heats of
formation for the reactants
Hr =  Hf products - Hf reactants
Consider the reaction : 2 NH3(g) + 5/2 O2 (g) ---> 3 H2O (g) + 2 NO (g)
Step 1
Record the Hf for each substance multiplying the values by the appropriate # of moles as seen in
the original equation
Step 2
Write the general equation for heat of reaction and substitute the values from above into the
equation and solve
Ex. 2
Calculate the  Hr for : C2H2(g) + 5/2 O2 (g) -----> 2 CO2 (g) + H2O (g)
Calculation of Heat of Formation Given the Heat of Reaction :
Consider the reaction : 4 C2H5NO2(s) + 9 O2(g) ---> 10 H2O(l) + 2 N2(g) + 8 CO2(g)
Hr = Heat of reaction = Heat of combustion = -973.49 kJ/moL
Calculate the Hf value for C2H5NO2
Step 1
Write the general equation for the calculation of heat of reaction
Step 2
Look at  Hf for each substance multiplying by the appropriate # of moles
Step 3
Substitute in the appropriate values into the general equation and solve for the unknown
Complete pg 332 (1a-d )pg 335 ( 2b,3 )pg 339 (8),pg 339(3)pg 340(4)
Research hot and cold packs
19
Problems on Hess’s Law
1. Calculate Ho/kJ for the following reaction using the listed standard enthapy of reaction data:
N2(g) + O2(g)
2 NO(g)
N2(g) + 2 O2(g)
2 NO(g) + O2(g)
2. Given the following equations and
N2(g) + O2(g)
2 NO(g)
4 NH3(g) + 5 O2(g)
4 NH3(g) + 3 O2(g)
3. Calculate
(C2H5)2O(l)
Ho/kJ = +66.4
Ho/kJ = -114.2
2 NO2(g)
2 NO2(g)
Ho values, determine the heat of reaction (kJ) at 298 K for the reaction:
6 H2O(l) + 4 NO(g)
2 N2(g) + 6 H2O(l)
Ho/kJ = -613
Ho/kJ = -790
Ho/kJ for the following reaction using the listed standard enthapy of reaction data:
C4H9OH(l)
C4H9OH(l) + 6 O2(g)
(C2H5)2O(l) + 6 O2(g)
4 CO2(g) + 5 H2O(g)
4 CO2(g) + 5 H2O(g)
4.Given the following equations and
C(s) + 2 H2(g)
CH4(g)
Ho/kJ = -2456.1 kJ
Ho/kJ = -2510.0 kJ
Ho values, determine the heat of reaction at 298 K for the reaction:
C(s) + O2(g)
CO2(g)
H2(g) + 1/2 O2(g)
H2O(l)
CO2(g) + 2 H2O(l)
CH4(g) + 2 O2(g)
Ho/kJ = -393.5
Ho/kJ = -285.8
Ho/kJ = +890.3
5. Given the following equations and Ho values, determine the heat of reaction at 298 K for the reaction:
C2H4(g) + 6 F2(g)
2 CF4(g) + 4 HF(g)
H2(g) + F2(g)
2 HF(g)
C(s) + 2 F2(g)
CF4(g)
2 C(s) + 2 H2(g)
C2H4(g)
Ho/kJ = -537
Ho/kJ = -680
Ho/kJ = +52.3
Calculating Heat of reaction (Hrxn) or Enthalpy of reaction
6. Use the given standard enthalpies of formation to determine the heat of reaction of the following reaction:
2 LiOH(s) + CO2(g)
Li2CO3(s) + H2O(l)
Hof
Hof
Hof
Hof
LiOH(s) = -487.23 kJ/mole
Li2CO3(s) = -1215.6 kJ/mole
H2O(l) = -285.85 kJ/mole
CO2(g) = -393.5 kJ/mole
7. Use the given standard enthalpies of formation to determine the heat of reaction of the following reaction:
2 Cl2(g) + 2 H2O(l)
4 HCl(g) + O2(g)
Hof H2O(l) = -285.8 kJ/mole
Hof HCl(g) = -92.3 kJ/mole
8. Calculate Hof (KJ) for the following reaction from the listed standard enthalpies of formation:
4 NH3(g) + 5 O2(g)
4 NO(g) + 6 H2O(g)
Hof NH3(g) = -46.1 kJ
Hof NO(g) = +90.2 kJ
Hof H2O(g) = -241.8 kJ
9. The standard enthalpy of formation of propane, C3H8, is -103.6 kJ/mole. Calculate the heat of combustion of
one mole of C3H8. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole
20
respectively.
10. The standard enthalpy of formation of propyne, C3H4, is +185.4 kJ/mole. Calculate the heat of combustion of
one mole of C3H4. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole
respectively.
11. The standard enthalpy of formation of ethanol, C2H5OH, is -277.7 kJ/mole. Calculate the heat of combustion
of one mole of C2H5OH. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole
respectively.
12. Given the following heat of reaction and the indicated heats of formation, determine the heat of formation of
B2H6(g) in kJ/mole.
B2H6(g) + 3 O2(g)
B2O3(s) + 3 H2O(g)
Ho = -1941 kJ
Hof B2O3(s) = -1273 kJ
Hof H2O(g) = -241.8 kJ
13. Using the given standard enthalpies of formation and the heat of reaction, calculate the heat of formation of
C2H2(g).
CaC2(s) + 2 H2O(l)
Ca(OH)2(s) + C2H2(g)
Ho = -127.2 kJ
Hof Ca(OH)2(s) = -986.2 kJ/mole
Hof CaC2(s) = -60.6 kJ/mole
Hof H2O(l) = -285.85 kJ/mole
Answers (kj/mol)
1.–180.6
2.+88.5
3.-54
4.–74.8
5.–2538.6
6.–133.5
7.+202
8.–906
9.+2220
10. +1940
11.
12.
13.
14.
+1370
–57.4
+226.7
+52
21
Energy Sources (pg 341)
1.
What 2 energy sources provide us with all our household and industrial energy needs ?
________________________________ and _____________________________
2.
Electricity comes from 3 major sources : _________________, ________________and
_____________________
3.
Complete Table below :
Source
Advantages
Hydroelectric
Fossil Fuels
Nuclear Energy
Complete page 355 ( 1-18),5,8,9,10,12,14,16 )
Disadvantages
22
Comparisons of various energy sources
Source
Coal
Nuclear
Hydroelectric
Gas / Oil
Advantages

Inexpensive

Easy to recover (in U.S. and Russia)

Fuel is inexpensive

Energy generation is the most
concentrated source

Waste is more compact than any source

Extensive scientific basis for the cycle

Easy to transport as new fuel

No greenhouse or acid rain effects

Very inexpensive once dam is built

Government has invested heavily in
building dams, particularly in the
Western U.S.
Disadvantages

Requires expensive air pollution controls
(e.g. mercury, sulfur dioxide)

Significant contributor to acid rain and
global warming

Requires extensive transportation system

Requires larger capital cost because of
emergency, containment, radioactive
waste and storage systems

Requires resolution of the long-term high
level waste storage issue in most
countries

Potential nuclear proliferation issue

Very limited source since depends on
water elevation

Many dams available are currently exist
(not much of a future source[depends on
country])

Dam collapse usually leads to loss of life

Dams have affected fish (e.g. salmon
runs)

Environmental damage for areas flooded
(backed up) and downstream

Very limited availability as shown by
shortages during winters several years
ago

Good distribution system for current use
levels

Could be major contributor to global
warming

Easy to obtain

Expensive for energy generation

Better as space heating energy source

Large price swings with supply and
demand


Wind is free if available

Good source for periodic water pumping
demands of farms as used earlier in
1900's
Wind

Generation and maintenance costs have
decreased. Wind is proving to be a
reasonable cost renewable source.

Need 3x the amount of installed
generation to meet demand

Limited to windy areas.

Limited to small generator size; need
many towers.

Need expensive energy storage (e.g.
batteries)
23

Solar
Biomass
Refuse Based
Fuel

Fusion
Sunlight is free when available

Industry in its infancy

Could create jobs because smaller plants
would be used

Fuel can have low cost

Could create jobs because smaller plants
would be used

Hydrogen
Well suited to rural areas.

Highly climate dependent - wind can
damage equipment during windstorms or
not turn during still summer days.

Can affect endangered birds, however
tower design can reduce impact..

Limited to southern areas of U.S. and
other sunny areas throughout the world
(demand can be highest when least
available, e.g winter solar heating)

Does require special materials for
mirrors/panels that can affect
environment

Current technology requires large
amounts of land for small amounts of
energy generation

Inefficient if small plants are used

Could be significant contributor to global
warming because fuel has low heat
content

Inefficient if small plants are used

Could be significant contributor to global
warming because fuel has low heat
content

Flyash can contain metals as cadmium
and lead

Contain dioxins and furans in air and ash
releases

Very costly to produce

Takes more energy to produce hydrogen
then energy that could be recovered.

Breakeven point has not been reached
after ~40 years of expensive research
and commercially available plants not
expected for at least 35 years.
Low sulfur dioxide emissions

Combines easily with oxygen to produce
water and energy

Hydrogen and tritium could be used as
fuel source

Higher energy output per unit mass than
fission

Low radiation levels associated with
process than fission-based reactors
24
Independent Research
Name ____________________
Analyse some conventional and alternative energy technologies (e.g., fossil fuel–burning power plants, hydropowered generators, solar panels, wind turbines, fuel cells), and evaluate them in terms of their efficiency and
impact on the environment Sample issue: The cooling of homes and commercial buildings in summer requires
more energy than heating in the winter at peak times. Brownouts are more likely in summer than in winter.
However, new technologies use deep lake water cooling as an alternative to conventional air conditioning
systems in office towers. This significantly reduces energy use and its environmental impact.
Questions:
1.
What proportion of Ontario’s energy needs is served by solar and wind technologies? What are the pros
and cons of expanding the availability of these technologies?
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
2.
What types of chemical reactions occur in different types of fuel cells?
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
3.
What are the advantages and disadvantages, in terms of efficiency and environmental impact, of using
corn to produce ethanol fuel?
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
Watch videos you tube : Solar and Wind Power - Renewable Energy Systems; How Fuel Cells
WorkGo to this web site and watch a series of videos http://www.ucsg.ca/index-4.html
25
Day 6
Assignment
Calculate each H using tables :
1.
2.
a)
CO2 (g) + H2 (g) -----------> CO (g) + H2O (g)
[ 41.2 kJ]
b)
C4H10 (g) + 13/2 O2 (g) --------> 4 CO2 (g) + 5 H2O (l)
[ -2874 kJ ]
Given: CH3COCH3 (l) + 4 O2 (g) -------> 3 CO2 (g) + 3 H2O (l)
H = - 1788.9 kJ
Find the Hf of CH3COCH3 (l) [ -249 kJ]
3.
Calculate the heat of formation,Hf, for ethane ,C2H6 (g) , from the following data:
Hc for C2H6 (g) = - 1555.0 kJ
Hf for CO2 (g) = - 393.0 kJ
Hf for H2O (l) = - 285.5 kJ
[ -89.4 kJ/mol ]
4.
In an experiment that uses a bomb calorimeter with a heat capacity of 10.42 kJ/C, a 0.46 g sample of
ethanol is burned in the presence of excess oxygen. The combustion reaction causes a temperature
increase from 21.48C to 22.79C. Calculate the heat of formation of ethanol.
[ -279 kJ]
5.
A calorimeter initially contains 125 g of water, at a temperature of 24.2C. 10.5 g of potassium
bromide, KBr, also at 24.2C, is added to the water, and the final temperature is 21.1C. Calculate the
heat of solution ( the enthalpy change accompanying the dissolution of the salt ) of potassium bromide
in J/g and in kJ/mol. Assume the specific heat capacity of the solution is 4.18 J/gC, and that no heat is
transferred to the surrounding or the calorimeter. [ 154 J/g, 20 kJ/mol ]
26
Calculate H for the reaction 2 N2 (g) + 5 O2 (g) -------> 2 N2O5 (g), given the data below.
6.
H = -285.8 kJ
H2 (g) + ½ O2 (g) -------> H2O (l)
N2O5 (g) + H2O (l) -------> 2 HNO3 (l) H = -76.6 kJ
H = -174.1 kJ
½ N2 (g) + 3/2 O2 (g) + ½ H2 (g) --------> HNO3 (l)
7.
[ H = 28 kJ ]
The bombardier beetle uses an explosive discharge as a defensive measure. The chemical reaction
involved in the oxidation of hydroquinone by hydrogen peroxide to produce quinone and water:
C6H4(OH)2 (aq) + H2O2 (aq) ---------> C6H4O2 (aq) + 2 H2O (l)
Calculate H for this reaction from the following data:
H = -203 kJ ]
H
H
H
H
C6H4(OH)2 (aq) ---------> C6H4O2 (aq) + H2 (g)
H2 (g) + O2 (g) ----------> H2O2 (aq)
H2 (g) + ½ O2 (g) --------> H2O (g)
H2O (g) ---------> H2O (l)
8.
=
=
=
=
+ 177.4 kJ
- 191.2 kJ
- 241.8 kJ
- 43.8 kJ
Using standard enthalpies of formation, calculate the enthalpy of reaction for each of the following:
a)
4 NH3 (g) + 7 O2 (g) -------> 4 NO2 (g) + 6 H2O (l)
[ - 1395 kJ ]
b)
3 Al (s) + 3 NH4ClO4 (s) -----> Al2O3 (s) + AlCl3 (s) + 3 NO (g) + 6 H2O (g)
[- 2673 kJ ]
Hf of NH4ClO4 (s) = - 295.3 kJ
9.
The Ostwald process for the commercial production of nitric acid from ammonia and oxygen
involves the following steps:
4 NH3 (g) + 5 O2 (g) ----------> 4 NO (g) + 6 H2O (l)
[ -1169.4 kJ]
2 NO (g) + O2 (g ) ------------> 2 NO2 (g)
[ - 114 kJ ]
3 NO2 (g) + H2O (l) ------------> 2 HNO3 (aq) + NO (g)
[ - 138.4 kJ ]
a)
Use the values of Hf to calculate the value of H for each step above.
b)
Write the overall equation for the production of nitric acid by combining the above reactions from
part a). Is the overall reaction exothermic or endothermic?
Overall reaction: NH3 (g) + 2 O2 (g) -------> HNO3 (aq) + H2O (l)
10.
[ -447 kJ, exothermic ]
The enthalpy of combustion of ethene gas, C2H4 (g), is -1411.1 kJ/mol at 298 K. Calculate the Hf
for ethene, given the following enthalpies of formation:
Hf for CO2 (g) = -393.5 kJ/mol
Hf for H2O (l) = -285.9 kJ/mol
[ 52 kJ/mol ]
27
Day 7 :
Rates Of Reaction ( pg. 360 )
Chemical Kinetics
-
study of reaction rates
Rate of a reaction
-
is the quantity of reactants consumed or the quantity of products formed
in a suitable unit of time.
the rate of a reaction is usually expressed in terms of a change in
concentration of one of the participants per unit time.
-
rate = [C ] /t = n
m
----= -------V x t
M x V x t
The rate of a reaction is the speed at which reactants are converted into products. Experiments show that for
most reactions, the []'s of all participants change the most rapidly at the beginning of the reaction. That is, the
[products] shows the greatest rate of increase and the [reactants] shows the greatest rate of decrease at the
beginning. This means that the rate of a reaction changes with time. Therefore a rate must be specified with a
specific time unit.
A + B ---> AB
Methods of Measuring Reaction Rates
Techniques used to measure concentration vary with the reaction and available apparatus. Titrations can be
done on reactions in solution. Changes in colour can be indications of concentration change and can be
measured in a spectrometer. Density and electrical conductivity may vary with concentration. For gases a
pressure change may tend to indicate a concentration change. The rate of a reaction is usually measured as a
function of the concentration of a reactant or product over time. This does not have to true in all cases. The
main feature of a rate is that it must be able to be measured physically. i.e. pressure, temperature,
concentration, colour and pH
Ex.1
Consider the reaction : Mg(s) + 2 HCl -----> MgCl2(aq) + H2(g)
It takes 20.0 s for 0.0480g of magnesium to disappear. What is the rate of disappearance of Mg and
what is the rate of appearance of H2? Assume 1.0 L container.
Ex.2
In measuring the rate of the reaction : 2 N2O5(g) ----> 4 NO2(g) + O2(g)
It was found that 8.00 x 10-4 moles of N2O5 per litre were used up during a period of 2.00 min. What is
the rate of reaction ; expressed as
a.
rate of disappearance of N2O5
b.
rate of appearance of NO2
c.
rate of appearance of O2
28
-
consider the graphs below : How is the rate of a reaction determine at any one instant ?
__________________________________. How is the average rate of a reaction determined ?
_________________________ How does the rate of a reaction change as the reaction progresses
toward completion and why ? _____________________________________________
Practice pg 361 (1,2) pg 364 ( 3,4)
b.
Monitoring Reactions ( pg 365 )
-
techniques used are change in colour, change in pressure, change in pH, disappearance of a solid
and the change in conductivity of a solution.
What techniques would be used to monitor these reactions :
1.
Zn(s) + 2H+(aq) -----> H2(g) + Zn+2(aq)
_________________________________
2.
C2H4(g) + Br2(g) ----> C2H4Br2(l)
_________________________________
Practice pg 365 ( 8 ) pg 366 ( 1 )
29
c.
Types of Reactions
1.
Homogeneous -
reactants are in the same phase
e.g 2H2(g) + O2(g) -----> 2 H2O(g)
2.
Hetereogeneous -
reactants are not in the same phase
e.g. 2 Na(s) + Cl2(g) ---> 2 NaCl(s)
d.
Factors Affecting The Rates Of Reactions
1.
3.
5.
Nature of Reactants
Temperature
Catalysts
pg 371 ( 2,4,5 ) pg 371 ( 1 )
2.
4.
6.
Concentration of reactants
Reaction mechanisms
Surface Area
30
Assignment
Name ____________________________________
Average and Instantaneous Rates
Practise using a graph to describe the rate of reaction as a function of the change of concentration
of a reactant and a product.
Use the following table to answer the questions regarding the equation below:
A + B  2C + D
Time (s)
[A] (mol/L)
0.00
3.20
0.00
3.00
2.42
1.58
6.00
1.95
2.50
9.00
1.63
3.14
12.00
1.40
3.62
15.00
1.23
3.94
18.00
1.10
4.18
1. (a)
[C] (mol/L)
On a set of concentration-time axes, plot a graph of [A] versus time. Use the grid below, a
separate sheet of graph paper, or a spreadsheet program.
(b) Explain the shape of the graph.
_____________________________________________________________________________
____________________________________________________________________________________________
(c) Draw a secant to the curve in the interval from t = 0.0 s to t = 3.0 s. Determine the slope of the
secant.
____________________________________________________
31
(d) What is the average rate of decrease of [A] from t = 0.0 s to t = 3.0 s?
_______________________________________________________
(e) What is the average rate of decrease of [A] between 3.0 s and 6.0 s?
_______________________________________________________
(f) How do you account for the difference in answers to questions (d) and (e)?
_________________________________________________________
(g) Draw a tangent to the curve at 6.0 s. Determine the slope of the tangent.
_________________________________________________________
(h) Interpret your answer for (g) in terms of rate.
_________________________________________________________
2. (a) On the same set of axes, plot a graph of [C] versus time (s).
(b) Explain the shape of the graph.
_______________________________________________________
(c) Draw a secant to the curve in the interval from t = 0.0 s to t = 3.0 s. Determine the slope of the
secant.
_______________________________________________________
(d) What is the average rate of increase of [C] from t = 0.0 s to t = 3.0 s?
________________________________________________________________
(e) What is the average rate of increase of [C] between 3.0 s and 6.0 s?
_________________________________________________________________
(f) How do you account for the difference in answers from questions (d) and (e)?
___________________________________________________________________
(g) Draw a tangent to the curve at 6.0 s. Determine the slope of the tangent.
____________________________________________________________________________
(h) Interpret your result for (g) in terms of rate.
3.
Based on the chemical equation for the reaction, write an expression that equates the rate of
reaction with respect to [A] to the rate of reaction with respect to [C].
______________________________________________
32
1.
-
Nature of Reactants ( pg 367 )
consider the reaction : 5C2O4-2 + 2MnO4-1 + 16H+ --> 10CO2 (g) + 2Mn2+ +8H2O
( covalent (purple)
(colourless)
bonds )
Reaction above is very slow; How would you monitor the rate of this reaction and why is it so slow ?
______________________________________________________________________________
consider the reaction : 5Fe2+ + MnO4-1 + 8H+ ---> 5Fe3+ + 2Mn2+ + 4H2O
-
How would you monitor this reaction and is it faster or slower than the one above ? Account
__________________________________________________________________________
Rules
1.
2.
3.
Reactions that do not involve bond rearrangements are usually rapid at room temperature.
Reactions in which bonds are broken tend to be slow at room temp.
It is usually impossible to predict the rate of a reaction merely by examining the chemical equation,
it must be done experimentally.
Try These :
1.
Predict the rate of the following :
a.
b.
c.
Cr2+ + Fe3+ -------> Cr3+ + Fe2+
Ba2+ + SO42- -------> BaSO4(s)
C8H18(l) + 12 1/2 O2(g) ----> 8 CO2(g) + 9 H2O(g)
2.
Consider the reaction :
_____________________________
_____________________________
_____________________________
C20H40(s) + 30 O2(g) -----> 20 CO2(g) + 20 H2O(g)
a.
If 1.00 moles of C20H40 is completely burned in 1.0 hr., What is the rate of the reaction expressed in
moles of O2 / Lxmin.(assume a 1.0L container)?
b.
Is this a heterogeneous or homogeneous reaction ?
c.
Give 2 reasons why it takes so long for the hydrocarbon to burn.
d.
How would you alter this hydrocarbon to make it burn more rapidly ?
33
1. Indicate the faster and slower reaction and explain why.
a) 2Al
+ 3I2 (s)
(s)
b) Ag+(aq)
2AlI3
→
+ Cl-(aq)
→
AgCl
(s)
(s)
2. Indicate the faster and slower reaction and explain why.
a) 2Al
(s)
b) 2Na+
+ 3I2 (s)
(aq)
2AlI3
→
+ 2ClO-
(aq)
→
2Na+
(aq)
(s)
+ 2Cl-(aq)
+
O2
(g)
3. Indicate the faster and slower reaction and explain why.
a) 3Ba+2(aq)
+
2PO4-3
(aq)
→
Ba3(PO4)2(aq)
b) Cu(s) + 2Ag+(aq)
→
Day 8
II.
Concentration of Reactants(pg 368)
-
for many reactions raising the concentration of a reactant increases the reaction rate
in a given amount of time, more collisions can occur in a concentrated mixture than in a less
concentrated mixture, thus # of effective collisions must increase
-
consider the demo : Solution A ( KIO3 ) is added to solution B ( Na2SO3 + starch ); by diluting the
KIO3 _____________ time required for the blue colour to appear i.e. ____________________
the rate of the reaction.
Rate Law pg 372
-
Cu+2 (aq)
+
2Ag
(s)
Consider the reaction : H2(g) + I2(g) -----> 2 HI(g)
violet
colourless
increasing [ H2 ] produces more H2 : I2 collisions per sec ; therefore reaction rate increases; also I2 has
similiar effect.
[H2] is doubled and I2 remains the same how should reaction rate change ___________________
34
Diagram :
H
I
H
H
I
H
-
If [I2] is tripled and H2 remains the same. How should reaction rate be affected?
Diagram :
-
Consider if both H2 and I2 are doubled.
Diagram :
Rate Law Expression ( pg. 373 )
-
consider the reaction : A + B ----> Products
Exp. #
[A]
[B]
Rate of formation of product
1
0.10
0.10
0.20
2
0.20
0.10
0.40
3
0.30
0.10
0.60
4
0.30
0.20
2.40
5
0.30
0.30
5.40
-
in exp. 1,2 and 3 the concentration of B is constant, therefore changes in rate are due to [ A ] only
in exp. 3,4 and 5 [ A ] is constant thus change in rate is due to [ B ] only.
-
Exp. 1 and 2 ----> [ A ] increases 2x; [ B ] is constant ; rate increases ______ x
rate is directly proportional to [ A ] -----
-
Exp. 3 and 4 ----> [ B ] increases 2 x ; [ A ] remains constant ; rate increases ______ X ;
rate is directly proportional to [ B ] ----rate law expression is : rate = k [ A ]---- [ B ]----k = proportionality constant ( rate constant ) ; varies with temp.
-
reaction order is determined by adding the exponents in the above equation ; thus reaction order is
_____________________________
solve for k for the above reaction :
k= ____________________________ = _______________________________________
35
Example 2 : 2 ICl + H2 ----> I2 + 2 HCl
Exp. #
[ICl]
[H2]
Rate of formation of I2
1
0.10
0.10
0.0015
2
0.20
0.10
0.0030
3
0.10
0.050
0.00075
Determine the rate law expression and determine the value and unit for k.
Example 3 : 2 H2 + 2 NO ----> 2 H2O + N2
Exp. #
[ H2 ]
[ NO ]
rate
1
5.0
1.0
0.40
2
5.0
2.0
1.6
3
1.0
5.0
2.0
4
3.0
5.0
6.0
Determine the rate law expression and determine the value of k.
Pg 377 ( 4,6 )
36
Rate Law Equations
Practise determining and interpreting rate law equations.
Answer the following questions about the rate law.
1. A chemist carries out three trials to determine the rate of the reaction of nitrogen dioxide and oxygen at
a fixed temperature. The chemist’s results are shown in the chart below.
NO2(g) + O2(g)  2N2O5(g)
Experiment
Initial [NO2]
(mol/L)
Initial [O2]
(mol/L)
Initial rate of
formation of N2O5
(mol/(L ÷ s))
1
0.025
0.011
3.1  10–4
2
0.025
0.022
6.2  10–4
3
0.050
0.011
6.2  10–4
(a) Write the rate law expression for the reaction. Explain your logic or show your calculations.
(b) Calculate the rate constant.
(c) A chemist runs a trial of the reaction (at the same temperature) in which the initial concentration of
[NO2] is 0.0323 mol/L and the initial concentration of [O2] is 0.0157 mol/L. Predict the initial rate.
37
2. A reaction has the following rate law:
Rate = k[A][B]2
Assuming a constant temperature, by what factor does the reaction rate change when the following
changes are made to initial reactant concentration?
(a)
[A] is tripled and [B] is doubled. How does the rate change?
(b)
[B] is halved and [A] remains the same. How does the rate change?
(c)
[A] is quadrupled and [B] is halved. How does the rate change?
(d)
[A] and [B] are halved. How does the rate change?
3. Consider the following reaction and its corresponding rate law:
BrO3–(aq) + 5Br–(aq) + 6H+(aq)  3Br3(aq) + 3H2O(l)
Rate = k[BrO3–][Br–][H+]2
(a)
What is the reaction order with respect to each reactant?
(b)
What is the overall order of the reaction?
(c) Suggest two different ways to track the rate of this reaction experimentally.
Collision Theory ( pg 383 )
-
for particles to react they must collide
rate = # of successful collisions/sec.
rate depends on :
a.
# of collisions per sec.
b.
fraction of these collisions that are effective
Successful Collision
i.
collision must be sufficiently energetic
38
ii.
#1
colliding particles must have proper orientation
energy may be sufficient but incorrect orientation
>
#2
Collision has the correct orientation but energy insufficient
>
#3
Collision is sufficiently energetic and the collision has the correct orientation:
>
39
- reactants collide together to form a temporary unstable complex " activated complex " which may separate
forming either the reactants or products
Day 9 :
Role of Energy in Reaction Rates (pg 383)
Collision Theory :
-
As 2 molecules approach very close to one another, the negative charges of the
electron clouds repel mutually and the speed of approach
; the
molecules with sufficient
energy continue to approach until 1
unstable particle is formed called the
; which may
separate into the 2 original molecules or into products.
The slowing down represents the continuous conversion of ___________________
energy into
energy.
potential energy is maximum in the
and decrease as the
resultant fragments separate
consider the reaction : H2 (g) + F2 = 2 HF (g) + Energy
as the reaction proceeds H - H and F - F bonds must be broken and new H - F bonds are formed. For
this process to take place molecules must collide, but collision must be sufficiently energetic and must
have favourable geometry.
Consider the Potential diagrams that follow : the path from reactants to products is not a direct one.
There is an energy hill whose height is identified as the
energy.
Height of barrier depends on nature of reactants i.e. types of bonds that have to be broken.
- the above reaction represents an _______________________________ reaction
What letter or letters represents ?
a.
Reactants _______b.
Products ________
c.
Activated complex ______
d.
Heat of reaction ( forward reaction ) ___________
h.
Relative energy of Reactants __
e.
Activation energy ( forward reaction ) ___________
i.
Relative energy of products___
f.
Activation energy of reverse reaction ____________
j.
Relative energy of A.C.______
g.
Heat of reaction ( reverse reaction ) _______________
Sketch a potential energy diagram for a reaction which has an E a of 60 kJ and a heat of reaction of + 20
KJ/moL. The Ea for the reverse reaction is _________ and the heat of reaction for the reverse reaction is
________________
40
-
Consider the following analogy : A pole vaulter approaches the bar.
a.
What represents the activation energy ?
b.
What 2 factors must be attained for a successful jump ? ___________________________
c.
At what position is the person most unstable ? Explain _______________________________
Day 10
IV
-
distribution of Kinetic Energies ( Maxwell - Boltzmann Curve ) : see pg 383
___________________________
Effect of Temperature( pg 368 ) (pg383)
Interpretations Of Curves
a.
Molecules have many different energies
b.
Most molecules have an energy value near that of the group average
c.
A few molecules have an energy value greater than the group average
d.
Increasing the temp. causes a general shift of the distribution toward higher kinetic energies
e.
Consider the red line call it Point A ( 30 kJ )represents the activation energy barrier - amount of
energy that must be exceeded in order for the molecules to react. A reaction can occur only if the
molecules of the reactants have sufficient kinetic energy to overcome the mutual repulsive forces
and form an intermediate " unstable " " activated complex "
Increasing the temp. increases the reaction rate, because more of the reacting molecules possess
sufficient energy for an effective collision. Rule of thumb is that the reaction rate doubles for every
10oC increase in temp. In the diagram the barrier is high thus only a few particles can react; this
represents a slow reaction . Analogy would be to pole vaulters trying to get over a very high height.
f.
Day 11
Lab : Rate of Reaction Pg 403
Day 12 :
Reaction Mechanism ( reaction that occurs in a series of steps ) ( pg. 387 )
-
most reactions proceed by a sequence of
, each involving only
particle collisions ( bi-molecular )
each of the steps is called an
step
the
step is the rate - determining step
the mechanism of a reaction cannot be determined from the net reaction ; it must be done
experimentally.
-
41
Ex.1
Consider the reaction : NO2 (g) + CO (g) ----> NO (g) + CO2 (g)
The following 2 step mechanism has been proposed :
i.
ii.
NO2 + NO2 -------> NO + NO3 ( slow step )
NO3 + CO -------> NO2 + CO2
a.
Add the equations to determine the net reaction. _____________________________________
b.
In determining the rate law consider only the slow step as long as no step comes before the slow
one ; if this case arises consider it as one slow step.
Since 2 NO2 molecules are in the slow step the rate law will include only NO2; intermediates nor
products will be considered when determining rate laws ;
rate law = k [ NO2 ]----
c.
The intermediate is
; which in most cases are very _______________
d.
If the [ NO2 ] were doubled , How would this affect the rate ? ______________
e.
If the [ CO ] were doubled ; What affect ? ___________________
f.
Suggest a reason why step i was the slowest
Example 2
4 HBr (g) + O2 (g) -----> 2 H2O (g) + 2Br2 (g) [ rapid ]
-
involves 4 HBr molecules for each O2 molecule
overall reaction brings together 5 molecules and the chances that 5 gaseous molecules will collide
simultaneously is almost zero but changes in concentration of HBr and O2 have equal effect even
though the ratio is 4 : 1 Why ? ______________________________________
_______________________________________
Mechanism
i.
HBr + O2 ------> HOOBr ( slow )
add :
ii.
HOOBr + HBr ----> 2 HOBr ( fast )
iii.
HOBr + HBr ----> H2O + Br2 ( fast )
iv.
HOBr + HBr -----> H2O + Br2 ( fast )
________________________________________________________________
a.
rate determining step is # ______________________________
b.
rate law = ____________________________________
c.
Doubling concentration of HBr should
d.
Doubling concentration of O2 should
e.
Doubling both should
f.
Why is step 1 the slowest step ?
g.
What order is the reaction ?
the rate
the rate
the rate
______________________________________
_______________________________
42
Ex.3
Imagine 5 people working together washing the dishes. 2 clear the table, 1 washes and rinses the
dishes and 2 dry them and stack them.
a.
b.
Which step is the rate determining step ? ____________________________________
How is the overall rate of the process affected if a 6 th person comes in to :
i.
ii.
iii.
Ex.4
help clear the table _________________________________
help to wash the dishes ________________________________
help to dry and stack __________________________________
Consider the following proposed mechanism :
A + B -----> C ( slow )
C + 2 A -------> D + E ( fast )
E ---------> F ( fast )
a.
What is the net reaction ? _______________________________________
b.
What is the rate law expression ? ___________________________________
Ex.5
Consider the following proposed mechanism :
NO + H2 -------> H2O + N ( fast )
NO + N -------> N2O ( slow )
N2O + H2 --------> N2 + H2O ( fast )
a.
b.
What is the net reaction ? __________________________________
What is the rate law expression ? _______________________________
Try the following :
-
the reaction H2(g) + I2(g) ----> 2 HI(g) is believed to occur in 2 steps :
i.
I2 -------> 2 I
H = + 150.6 kJ/moL
Ea = 180 kJ
ii.
2I + H2 ----> 2 HI
H = - 98.7 kJ/moL
Ea = 400 kJ
a.
b.
Show how the 2 steps add up to give overall reaction. ____________________________________
What is the overall Hr and is this an endothermic or exothermic reaction ? ___________________
c.
Considering the mechanism above what is the rate determining step and what is the rate law
equation ? __________ _____________________________
d.
Sketch the P.E. diagram for the above; show values for heats of reaction for each step and Ea for
each step and the overall heat of reaction.
43
Practice pg 390 ( 2 ) pg 391 ( 2,3 )
44
Day 13
1.
Reaction Equations & Mechanisms
The following mechanism has been proposed for the reaction between iodobutane and chloride ion:
step 1: C4H9I -------------> C4H9+ + Istep 2:
C4H9+ + Cl- ----------> C4H9Cl
a) Give the overall equation for the reaction.
__________________________________________
b) Identify any reaction intermediates.
__________________________________________
c) If step 2 is the rate determining step, write the reaction rate equation. _____________________________
2.
The following mechanism has been proposed for the reaction between nitrogen dioxide and
methane:
step 1:
NO2
+ NO2 -------------> NO3
+
NO
step 2:
NO3
+ CH4
-------------> HNO3 + CH3
step 3:
CH3
+ NO2
------------->
CH3NO2
a) Give the overall equation for the reaction.
____________________________________________
b) Identify any reaction intermediates.
_____________________________________________
c) If step 2 is the slowest step, write the reaction rate equation. ___________________________________
3. The decomposition of ozone, O3, is believed to occur by the two-step mechanism
O3 -----> O2 + O (slow) O + O3 -----> 2 O2 (fast) 2 O3 -----> 3 O2 (net reaction)
If this is the mechanism, what is the reaction's rate law?
_________________________________
Review: Rate Laws
1.
OCl- + I- -----> Cl- + OI- It is a rapid reaction that gives the following rate data.
Initial Concentrations ( mol/ L )
Rate of Formation of Cl-
[ OCl- ]
[ I- ]
( mol L-1 s-1 )
1.7 x 10-3
1.7 x 10-3
1.75 x 104
3.4 x 10-3
1.7 x 10-3
3.50 x 104
1.7 x 10-3
3.4 x 10-3
3.50 x 104
What is the rate law for the reaction? Determine the value of the rate constant.
45
2.
The formation of small amounts of nitric oxide, NO, in automobile engines is the first step in the
formation of smog. Nitric oxide is readily oxidized to nitrogen dioxide by the reaction :
2 NO(g) + O2(g) -----> 2 NO2(g).
The following data were collected in a study of the rate of this reaction.
Initial Concentrations ( mol/ L )
Rate of Formation of NO2
[ O2 ]
[ NO ]
( mol L-1 s-1 )
0.0010
0.0010
7.10
0.0040
0.0010
28.4
0.0040
0.0030
255.6
What is the rate law for the reaction? What is the rate constant? Propose a mechanism from the
reaction.
3.
At a certain temperature the following data were collected for the reaction:
2ICl + H2 ---> I2 + 2HCl
Initial Concentrations ( mol/ L )
Rate of Formation of I2
[ICl]
[ H2 ]
( mol L-1 s-1 )
0.10
0.10
0.0015
0.20
0.10
0.0030
0.10
0.050
0.00075
What is the rate law, rate constant, and proposed mechanism for this reaction?
4.
The following data were obtained for the reaction:
(CH3)3CBr + OH- ------> (CH3)3COH + Br Initial Concentrations ( mol/ L )
Rate of Formation of (CH3)3COH
[ (CH3)3CBr ]
[ OH- ]
( mol L-1 s-1 )
0.10
0.10
1.0 x 10-3
0.20
0.10
2.0 x 10-3
0.30
0.10
3.0 x 10-3
0.10
0.20
1.0 x 10-3
0.10
0.30
1.0 x 10-3
What is the rate law, rate constant, and proposed mechanism?
46
5.
Consider the reaction: NO2 + CO ------> CO2 + NO
[NO2]
[CO]
rate
0.01
0.01
2.1 x 10-8
0.02
0.02
8.40 x 10-8
0.04
0.02
3.36 x 10-7
0.02
0.04
8.4 x 10-8
What is the rate law, rate constant, and propose a mechanism.
6.
Consider the reaction: 4 OH + H2S ------> SO2 + 2 H2O + H2
[OH]
[H2S]
rate
1.3 x 10-8
2.1 x 10-8
1.4 x 10-6
3.9 x 10-8
2.1 x 10-8
4.2 x 10-6
3.9 x 10-8
4.2 x 10-8
8.4 x 10-6
What is the rate equation? Calculate the rate constant.
Day 14 :
Consider the following mechanism :
Elementary Step
Activation Energy
Heat of Reaction
A + B2 --> AB2
+4.0 kJ/moL
- 10.0 kJ/moL
AB2 + C2 --> ABC + BC
+30.0 kJ/moL
+ 5.2 kJ/moL
ABC + B2 --> AB2 + BC
+ 10.0 kJ/moL
- 7.8 kJ/moL
a.
What is the overall reaction ? _______________________________
b.
Which step is the rate determining step and how can you tell ? ____________________________
c.
What is the rate law expression for this reaction ? ___________________
d.
What is the overall Heat of Reaction ?
e.
Draw a potential energy diagram for the above ; label all the data.
_________
47
Consider the diagram below and answer the questions that follow :
a.
Which step is the rate determining step ? _____________ why ? __________________
b.
What is the Ea for the first step ? ____________ Heat of reaction = _________________
c.
Which is the fastest step ? _______________ Why ? ______________________
d.
what is minimum activation needed to run this reaction ? __________________
e.
What is X ? ________________ What is W ? ________________________
f.
What is the overall heat of reaction ? _____________________________
V
Catalysts(pg 369,395)
-
substances that increase the rate of the reaction without being used up itself
makes possible a different reaction mechanism having a ______________activation energy; since
P.E. of reactants and the products remains the same the ________________
remains the same.
-
this represents an ____________________________ reaction ; the dotted line represents how a
________________ affects the rate of the reaction.
48
Types of Catalysts
1.
Homogeneous -
one that is in the same phase as the reactants
e.g. the decomposition of methanoic acid is very slow :
HCOOH -----> H2O + CO ( very slow )
H2SO4 is added as the catalyst :
i.
A proton is transferred from the sulfuric acid to the methanoic acid
ii.
Intermediate molecule comes apart splitting out water and forming a second intermediate
iii.
A proton is transferred from the intermediate to HSO4- forming CO and regenerating H2SO4
II.
Heterogeneous catalyst -
-
different phase than reactants
reactants are adsorbed and are bonded temporarily to the surface ; this weakens the bonds between
reactant molecules thus less Ea is needed for the reaction ; also known as surface catalyst e.g. Pt, Pd,
Fe
e.g.
-
2 CO(g)
+
O2(g)
--------> 2 CO2(g)
catalyst used in catalytic exhaust converters is an alloy of platinum and palladium thinly coated
on a porous inert material. When an oxygen molecule is adsorbed on the surface its bonds are
weakened and break. This reduces the activation energy for the reaction when a molecule of CO from
the exhaust gases unites with the atomic oxygen to form CO 2. When the CO2 leaves the surface of the
catalyst, the surface is again bare and ready for repetition o the process
49
Question
1.
Consider the following reaction mechanisms:
Step 1: NO2+ Mn -----> NO2Mn
Step 2: NO2Mn + NO2-----> NO3+ NO + Mn
Step 3: NO3 + CO -----> NO2 + CO2
a)
Identify a catalyst.
________________________________
b)
Identify a reaction intermediate.
c)
Identify the products of the overall reaction. What is the net reaction ? ____________________
___________________________________________________
____________________________
50
Chemistry of Ozone Depletion by CFCs ; watch video www.teachersdomain.org Ozone Hole

What is ozone and why do we need it in our atmosphere to have a healthier planet?
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

Describe how ozone protects us.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

How is a chlorine atom harmful to the ozone in the stratosphere?
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

CFCs (chloroflourocarbons) are molecules that are harmful to the atmosphere. How are CFCs getting into
our atmosphere and how can humans prevent a continuous increase?
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
51
Independent Research
-
Analyse the conditions (e.g temperature, pressure, presence of a catalyst) required to maximize the
efficiency of some common natural or industrial chemical reactions ( e.g. decomposition,
combustion, neutralization and explain how the improved efficiency of a reaction contributes to
environmental sustainability. Bleaches such as hydrogen peroxide and chlorine are used when fibres
are processed into paper or textiles. Concentrations of these substances can harm the environment
but if enzymes are added to these processes as biocatalysts fewer chemicals are needed, less
energy is consumed and there is less environmental impact.
Questions to consider :
1. How can you increase the rate of decomposition in a home composter.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
2. What can be done to improve the efficiency of an automobile that runs entirely on fossil fuels
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
3.
Why is just a very small quantity of catalyst required in industrial processes.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
4. Why is the ozone layer still deteriorating despite the banning of CFCs.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
52
Day 15
-
5.
Surface Area (pg 370,393)
an increase in the area of a solid reactant _________________ reaction rate. More particles are exposed
to surface increasing chances of collision.
Consider a 2 cm cube of Aluminum
1.
What is the total surface area of the cube ? _______________________________________
2.
If the cube was divided into 8 smaller cubes each ( 1cm x 1cm x 1cm ). What would be the total
exposed surface area of the Al now and theoretically what would be the increase in reaction rate.
_______________________________________________________________________________
Watch video on www.teachersdomain.org : Dust Explosion
Complete Pg 407 (1-18),5,6,7,8,10,11,15,16)
Review :
1.
Why do wood shavings burn more rapidly than a log ?
____________________________________
2.
Why do fuels burn more rapidly in pure oxygen than in air? __________________________________
3.
Aluminum metal is used on the exterior of buildings yet a bottle of Aluminum powder is labelled
flammable. Explain. __________________________________________________________________
4.
Given the following reaction : FeS(s) + 2 HCl(aq) -----> FeCl2(aq) + H2S(g)
List changes that could be made to this system to increase the rate and how would you monitor this
reaction.
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
53
RATES OF REACTION : Review
1.
A reaction has the following mechanism :
Step 1
A + B -------> C + E
Ea(kJ/moLA)
+ 45
Step 2
A + E -------> 2 D
+ 80
ΔH(kJ/moL
-72
+28
a.
Write the overall chemical equation.
____________________________________
b.
Explain the meaning of the term rate determining step. _________________________________
c.
Which step above is the rate determining step ? Why ? __________________________________
d.
What is the rate law equation for the mechanism above i.e. rate = k [ ] _____________________
e.
What effect would doubling the concentration of A have on the overall rate ; How about doubling
[B].
__________________________
____________________________
f.
What is the overall ΔH for the above mechanism. _________________ ; min. Ea _____________
g.
Plot a P.E. diagram for the above mechanism ; label Ea and the ΔH for each step and the overall ΔH
for the reaction.
2.
Consider the following reaction and the experimental data :
2 NO (g) + H2(g) -----> N2O (g) + H2O (g)
[NO]
[H2]
0.075
0.150
0.150
0.400
0.200
0.400
rate of reaction(moL/Lxmin.)
0.005
0.010
0.0200
a.
Find the rate law expression
b.
Determine the value of the rate constant . _______________________________________
c.
Propose a mechanism consistent with the rate law
3.
If the mechanism for a reaction is :
A + B ----> C
D + A ----> F
a.
_________________________________________
+
+
__________________________________________
D ( slow )
F ( fast )
Write the overall equation.
___________________________________________
54
b.
4.
Write the rate law expression that is consistent with the proposed mechanism .
The mechanism for a reaction is given by :
NO2Cl -----> NO2
Cl + NO2Cl -----> NO2
5.
+ Cl ( slow )
+ Cl2
a.
Write the overall equation.
________________________________________
b.
What is the intermediate ?
________________________________________
c.
What is the rate law expression and what is the order of this reaction ?
At low pressures, the reaction :
2 NO2 + F2 -------> 2 NO2F follows the rate law : rate = k[NO2][F2]. Suggest a
mechanism and indicate the slow step.
6.
Consider the reaction : 2A + B ----> C and the data below :
[A] [B]
Rate(moL/Lxmin.)
0.10 0.10
0.20 0.10
0.30 0.10
0.20 0.20
0.30 0.30
2.0
8.0
1.8
8.0
1.8
x
x
x
x
x
10-3
10-3
10-3
10-3
10-3
a. Write the rate equation for the reaction above.
b. Calculate the rate constant.
c. Postulate a two - step mechanism that is in agreement with the data.
7.
Consider the proposed mechanism
H2O2 + I- ----> H2O + OI- ( slow )
H+
+ OI- -----> HOI ( rapid )
HOI + H+ + I- ------> I2 + H2O ( rapid )
a. What is the net reaction ?
b. What is the rate law equation ?
55
8.
Consider the reaction : A ---> B ; Ea = + 30kJ/moL ; ΔH = -20kJ/moL
a. Plot a potential diagram for this reaction and label the values above .
b. Is the forward reaction endothermic or exothermic ?
______________________
c. What energy values would change if a catalyst were added?
______________________
d. What happens to the Ea value if the temperature is increased ? _____________________
9.
Formic acid reacts with bromine as follows :
HCOOH (aq) + Br2(aq) -----> CO2(g) + 2H+ + 2Br-(aq)
The initial concentration of Br2 was 10.0 moL/L. After 2.5 min. the concentration of Br2 was
6.2 moL/L.
a.
What is the rate of the reaction in terms of consumption of Br2 ? __________________
b.
Express the rate in terms of appearance of Br- ions. ____________________________
When H2(g) and O2(g) are mixed at 22oC there is no reaction , yet when platinum is introduced an
explosion occurs . Explain this observation with a series of diagrams including a Kinetic energy
diagram plus a diagram showing how an hetereogeneous catalyst works .
10.
Day 16 :
Complete pg 412 (1-30)(omit 8 )
Pg 414 (2,3,4,5,6,7,12,13,14,15,16,18,19,20,21,22,23,26)
56
UNIT 3 REVIEW
1.
The combustion of methanol is shown by the following equation:
i. Given the data which follows:
a. Find the heat of reaction for the equation above.(-478 kJ)
b. State the molar heat of combustion of methanol.(-239 kJ/mol
c. State whether the reaction is endothermic or exothermic.
ii.What mass of water could be heated from 20.0 0 C to 35.00 C by the burning of 2.57 mol of methanol? (
2.
)(
9.78 kg )
Ethanol, C2H5OH, is made industrially by the reaction of water with ethylene, C 2H4. Calculate the value of Ho for the reaction (-44 kJ )
C2H4(g) + H2O(l)  C2H5OH(l)
given the following thermochemical equations:
C2H4(g) + 3 O2(g)  2 CO2(g) + 2 H2O(l) Ho = –1411.1 kJ
C2H5OH(l) + 3 O2(g)  2 CO2(g) + 3 H2O(l) Ho = –1367.1 kJ
3.
If one mole of water absorbs 44 kJ of heat as it changes state from liquid to gas, calculate the amount of heat that is absorbed if 200 g of
water is evaporated.( 4.9 x 102 kJ )
4.
Hydrogen peroxide decomposes to form oxygen gas and water. The rate of the reaction was studied at a particular temperature. The
following data was obtained (0.0023 mol/(L·s))
Initial Concentration (
Final Concentration (
)
)
Time Elapsed
0.200 mol/L
0.154 mol/L
20 s
What was the average rate of decomposition?
5.
The initial rate of the reaction: BrO3-(aq) + 5 Br-(aq) + 8 H+(aq)  3 Br2(l) + H2O(l)
Has been measured at the reactant concentrations shown (in mol/L)
Experiment
1
[BrO3-]
0.10
[Br-]
0.10
[H+]
0.10
Initial rate (mol/(L·s))
2
3
4
0.20
0.10
0.10
0.10
0.20
0.10
0.10
0.10
0.20
1.6  10-3
1.6  10-3
3.2  10-3
8.0  10-4
According to these results, what would be the initial rate (in mol/(L·s)) if all three concentrations are: [BrO 3-]=[Br-]=[H+]=0.20 mol/L?
(1.28 x 10-2 mol/(L·s)).
6.
The decomposition of ozone, O3, is believed to occur by the two-step mechanism
If this is the mechanism, what is the reaction's rate law? (The rate law must be r = k[O3]1 )
57
7.
Given equations (1) and (2), calculate the enthalpy change for equation (3).509 kJ/mol.)
(1) Pb(s)  PbO2(s)  2SO3(g)  2PbSO4(s)
H  775 kJ
(2) SO3(g)  H2O(l)  H2SO4(aq)
H  133 kJ
(3) Pb(s)  PbO2(s)  2H2SO4(aq)  2PbSO4(s)  2H2O(l)
8.
1.435 g of naphthalene (C10H8) is burned in a bomb calorimeter. There is exactly 2000.0 g of water surrounding the naphthalene. The
temperature of the water rises from 20.17C to 25.85C. The heat capacity of the bomb calorimeter is 1.80 kJ/C.
a) What is the heat change for the burning of naphthalene? –57.7 kJ.
b) What is the heat of combustion of naphthalene? –5.15  103 kJ/mol.
c) Write the thermochemical equation. C10H8(l)  12O2(g)  10CO2(g)  4H2O(l)  5.15  103 kJ/mol
9.
0.412 g of calcium reacts in a coffee-cup calorimeter that contains 200.0 g of water. The initial temperature of the water is 18.9C, and
the final temperature is 24.0C. Calculate the standard molar enthalpy change for this reaction. 4.14  102 kJ/mol Ca.
10.
A chemist uses a coffee-cup calorimeter to neutralize completely 75.0 mL of 6.67 mol/L HCl with 75 mL of NaOH. The temperature
change is 39.6C.
a) Calculate the heat of neutralization, in kJ/mol of HCl. 49.8 kJ
b) Write a thermochemical equation for the reaction. ) HCl(aq)  NaOH(aq)  NaCl(aq)  H2O(l)  49.8 kJ
11.Given equations (1), (2), and (3), calculate the heat of reaction for equation (4).
(1)
N2(g)  H2(g)  NH3(g)
Hf  46.15 kJ
(2)
N2(g)  O2(g)  NO2(g)
Hf  33.81 kJ
Hf  241.6 kJ
(3) H2(g)  O2(g)  H2O(g)
(4) NH3(g)  O2(g)  NO2(g)  H2O(g)
NH3(g) 
O2(g)  NO2(g) 
H2O(g)
H°f  281.9 kJ
12.
Use standard heats of formation and the following equation to determine the enthalpy of formation of C 2H6(g).
2C2H6(g)  7O2(g)  4CO2(g)  6H2O(l) Hrxn  3127 kJ is 80.9 kJ/mol C2H6(g).
13.
Quicklime or lime, CaO, is widely used in the building and steel industries. In the past, lime was difficult to transport because of its
exothermic reaction with water. Several ships caught on fire when water leaked in and reacted with the lime.
CaO(s)  H2O(l)  Ca(OH)2(aq)
H  –65.2 kJ/mol
If a 500 g sample of water reacted with 10.0 g of quicklime, what would the final temperature be? Assume that the calcium hydroxide
solution absorbed all the heat released. Also assume that the initial temperature of both the water and the quicklime was 25C. The
specific heat capacity of calcium hydroxide solution is 1.20 J/gC. The final temperature of the solution would be 44C.
14.
Plants produce glucose from carbon dioxide, water, and sunlight.
6CO2(g)  6H2O(l)  C6H12O6(s)  6O2(g)
a) The heat of formation of glucose is 1274.5 kJ/mol. Use this heat of formation, and standard enthalpies of formation, to determine
how much energy is needed from the Sun to make one mole of glucose. 2801 kJ/mol C6H12O6(s)
b) Plants produce about 7.0  1014 kg of glucose a year, using solar radiation. How much solar radiation is used? 1.09  1019 kJ of
energy.
15.
The Bombardier beetle defends itself by squeezing fluid from an inner compartment to an outer compartment. In the outer compartment,
an exothermic reaction takes place in the presences of enzymes.
C6H4(OH)2(aq)  H2O2(aq)  C6H4O2(aq)  2H2O(l)
Determine the heat of reaction, using the following equations. is 204 kJ/mol.
C6H4(OH)2(aq)  C6H4O2(aq)  H2(g)
H  177 kJ
H2O2(aq)  H2O(l)  O2(g)
H  94.6 kJ
H2(g)  O2(g)  H2O(l)
H  286 kJ