Thermochemistry &
Rates Review
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TITLE C
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TITLE D
Thermochemistry
& Rates
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The units for enthalpy change are:
a. kJ
c. kJ/mol
b. kJ/kg•°C
d. kJ/L•°C
1A Answer 100
a. kJ
Q2A Question 200
What is the unit of rate constant, K, if it is a second- order
reaction and the rate is measured in mol/L.s and
concentrations in mol/L
2A ANSWER 200
K= L/mol
Q3A Question 300
In the reaction: CH4 +2O2  CO2 + 2H2O
The rate of consumption of oxygen gas is observed to be 4
mol/(L.min). What is the rate of production of CO2 gas?
a)1 mol/(L.min)
b) 2 mol/(L.min)
c) 4 mol/(L.min)
d) 8 mol/(L.min)
3A ANSWER 300
b) 2 mol/(L.min)
Q4A Question 400
The rate of reaction depends upon:
a)The concentration and nature of the reactant
b)The temperature of the reaction
c)Whether or not a catalyst was used
d)All of the above
4A Answer 400
d)All of the above
Q5A Question 500
Which of the following factors that affect rate of reaction applies
only to heterogenous system
a)
Surface area
b)
Concentration
c)
Temperature
d)
catalyst
5A Answer 500
a)Surface area
Q1B Question 100
The catalytic converter on a vehicle is:
a)
A biological catalyst
b)
Heterogenous catalyst
c)
A homozygous catalyst
d)
A reactant
1B Answers 100
a) Heterogenous catalyst
Q2B Question 200
The activation energy of a chemical reaction is affected by:
a)
The kinetic energy of the reactant
b)
The potential energy of the product
c)
The presence of a catalyst
d)
None of the above
2B Answer 200
a)
The presence of a catalyst
Q3B Question 300
If the initial rate of reaction is observed to increase by a factor of
9 when the concentration of a reactant is tripled, what is the
order of reaction with respect to the reactant
a) 0
b) 1
c) 2
d) 3
3B Answer 300
c) 2
Q4B Question 400
The gas phase reaction A + B C has a reaction rate that is
experimentally observed to follow the relationship: rate =
K[A]2. What is the reaction order with respect to B
a) 0
b) 1
c) 2
d) 3
4B Answer 400
a) 0
Q5B Question 500
Which of the following statement is incorrect?
a) The reaction rate for a zero-order reaction is independent of
the concentration
b) The rate constant for a second-order reaction is dependent
on temperature
c) The rate law expression relates rate and concentration
d) The rate constant for a first-order reaction never varies with
temperature or pressure
5B Answer 500
d) The rate constant for a first-order reaction never varies with
temperature or pressure
Q1C Question 100
• Which of the following corresponds to the equation for the
standard molar enthalpy of formation of solid sodium
chlorate, NaClO3
a.Na(s) + 1/2 Cl2(g) + 3/2O2 → NaClO3(s)
b. 2Na(s) + Cl2(g) +3O2(g) →2NaClO3(s)
c. Na(s) + Cl(g) + 3O(g) → NaClO3(s)
d. NaCl(s) + 3/2 O2(g) → NaClO3(s)
1C Answer 100
a. Na(s) + 1/2 Cl2(g) + 3/2O2 → NaClO3(s)
Q2C Question 200
Which of these describes a reaction intermidiates
a) Starting material
b) A product
c) Something formed and consumed during a reaction
d) A step in a reaction mechanism
2C Answer 200
c) Something formed and consumed during a reaction
Q3C Question 300
How many Kilojoules of heat is necessary to decompose 90 g of
H2O(g) into H2(g) and O2(g) at ambient temperature and pressure
H2(g) + O2(g) → H2O (g)
a)48.1 kJ
b)120.9 kJ
c)241.8 kJ
d)1208 kJ
∆Hof = -241.8KJ
3C Answer 300
d) 1208 kJ
Q4C Question 400
In a coffee-cup calorimeter, 50 ml of 1.0 mol/L HCl was neutralized by
50 ml of 1.0 mol/L NaOH. Initial temperature of both solutions were
24.5oC. Final temperature after the reaction was 75.5oC.
1.
2.
3.
4.
5.
6.
Was the reaction exothermic or endothermic? Explain
Calculate the mass of both solutions
Calculate the temperature change
Determine the thermal energy, q, released by the reaction.
Calculate the number of moles of base in the reaction
Calculate the molar enthalpy of neutralization, ∆Hneut. Of the base.
4C Answer 400
1. Exothermic reaction. Increase in temperature of the
surrounding
2. 50 gm each
3. 75.5 oC– 24.5oC = 51oC
4. q =mc∆t =100g x4.18J/g.oC x51oC = - 21.32kJ
5. n = C xV(L) =1.0mol/L x 50 ml/1000ml = 0.05 mol
6. q = ∆H = n∆Hneut; q = n∆Hneut
∆Hneut = q/n
= - 21.32kJ
0.05 mol
- 426.4 kJ/mol
Q5C Question 500
. In a coffee cup calorimeter, you place 15.0 mL of distilled
water and measure the starting temperature to be 25C. You
then place 2.44 g of an unknown metal (initially heated up to
99.8C) into the distilled water and insulate the calorimeter.
After equilibrium, the final temperature of the water and the
unknown metal is 26.1C.
What is the specific heat (in J/gC) of the unknown metal? The
specific heat of water is 4.184 J/gC. Assume that no heat is
transferred to the calorimeter. Show your starting equations,
all of your calculations, and box in your final answer.
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mw =15 ml x1 g/ml
=15 g water
t1w = 25 oC
t2w = 26.1
∆t w = t2 – t1
= 26.1oC – 25oC
=1.1 o C
cw = 4.18J/g x oC
qw =mc∆t
= 15 g x 4.18J x1.1oC
g x oC
= 68.97 J
m unknown m = 2.44 g
t1metal = 99.8 oC
t2 metal = 26.1oC
∆t metal = 26.1oC – 99.8 oC
-qmetal = qwater
(2.44 g x c x -73.7 oC) =68.97 J
c = 68.97 J
179.828 gxoC
0.3835 J/g.oC
Q1D Question 100
For the reaction: A + 2B → 3C
When the rate of appearance of C is 9 x 10-7 mol/L.s, What will
be the rate of disappearance of B?
a) 2 x 10-7mol/L.s
b) 12 x 10-7 mol/L.s
c) 6 x 10-7 mol/L.s
d) 9 x 10-7 mol/L.s
1D Answer 100
c) 6 x 10-7 mol/L.s
Q2D Question 200
In a reaction mechanism, the rate determining step is always:
a) The last step
b) The slowest step
c) The reaction intermediate
d) The fastest step
2D Answer 200
b) The slowest step
Q3D Question 300
True or false
The instantaneous reaction rate is always constant.
3D Answer 300
False
Q4D Question 400
Pyruvic acid is a molecule involved as an intermediate in
metabolic reactions such as cellular respiration. Pyruvic acid
(CH3COCOOH) is converted into acetic acid and carbon monoxide
in the reaction:
CH3COCOOH  CH3COOH + CO
If the molar enthalpies of combustion of these substances are,
respectively –1275 kJ/mol, -875 kJ/mol, and -282.7 kJ/mol, use
Hess’s law to calculate the enthalpy change for the given
reaction. [Hint: write equations to represent the combustion
reactions for the reactant and products. The given reaction
above is the target equation]
1. CH3COCOOH + 5O2 → 3CO2 + 2H2O ∆HCom = –1275 kJ
-1 x 2. CH3COOH + 2O2 → 2CO2 + 2H2O ∆HCom = 875 kJ x-1
-1 x 3. CO + 1/2O2 → CO2
∆HCom = 282.7 kJ x-1
1. CH3COCOOH + 5/2O2 → 3CO2 + 2H2O ∆HCom1 = –1275 kJ
2. 2CO2 + 2H2O → CH3COOH + 2O2 ∆HCom2 = 875 kJ
3. CO2 → CO + 1/2O2
∆HCom3 = 282.7 kJ
Cancel molecules common to both sides
Sum up the molecules and enthalpy change of three reactions:
∆H =∆H Com1 + ∆HCom2 + ∆HCom2
CH3COCOOH  CH3COOH + CO
∆Hr = 117.3 KJ
Q5D Question 500
A certain chemical reaction can be represented by the following equation.
2A(g) + B(g) → C(g)
At a fixed temperature, the initial rate of the reaction was measured for
various initial concentrations of A and B. The results were as follows:
Initial Conc. (mol/L) Initial reaction Rate (mol/L.s)
A
B
0.5
0.5
2.0 x 10-3
1.0
0.5
8.0 x 10-3
1.0
1.0
8.0 x 10-3
1.5
1.0
18 x10-3
1.0
1.5
8.0 x 10-3
• The rate law expression for this reaction is
a) Rate = K[A][B]
b) Rate = K[B]2
c) Rate = K[A]2[B]2
d) Rate = K[A]2
5D Answer 500
d) Rate =
2
K[A]
Q1E Question 100
Similar elements tend to react similarly, but at different reaction
rate.
1E Answer 100
True
Q2E Question 200
The heat released during the combustion of C3H8(g) (propane)
to produce CO2(carbon dioxide) gas and water vapour is
2222 kJ/mol of C3H8(g). Which of the following is the correct
chemical equation for the reaction?
a. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O (g) ∆H = +2222 kJ
b. C3H8(g) + 5O2(g) + 2222 kJ → 4H2O (g) + 3CO2(g)
c. C3H8(g)+ 5O2(g) →3CO2(g) + 4H2O (g) + 2222 kJ
d. 3CO2(g) + 4H2O(g) → 5O2(g) + C3H8(g) = ∆H 2222 kJ
2E Answer 200
c. C3H8(g)+ 5O2(g) →3CO2(g) + 4H2O (g) + 2222 kJ
Q3E Question 300
According to the Rate Law, the rate (r) for the reaction
aX +bY → product must be proportional to:
a. [X]
c. [X]a[Y]b
b. [Y]
d. [X]m[Y]n
3E Answer 300
d.
m
n
[X] [Y]
Q4E Question 400
Consider the decomposition of hydrogen peroxide reaction. If
the rate of decomposition of hydrogen peroxide at a particular
temperature is determined to be 0.098 mol/(L·s), what are
the rates of reaction with respect to the products of the
decomposition reaction?
[Hint: Be sure to write a balanced chemical equation to
represent the reaction]
4E Answer 400
H2O2(l) → H2(g) + O2(g)
∆[H2O2(l)] = 0.098 mol/(L.s)
∆t
∆[H2O2(l)] = [H2(g)]
∆t
∆t
= [O2(g)]
∆t
[H2(g)] = 0.098 mol/L.s
∆t
[O2(g)] = 0.098 mol/L.s
∆t
Q5E Question 500
Insert Daily double question or
picture here.
5E Answer 500
Insert answer or picture
choice here!