Tentative Chapter Five Assignments and Schedule
Date
Problems
Comments
Video Due
Day One
Book
Sections
5.1-5.3
2,4,17,23,25
Intro to Energy
THT from Ch4 due
0
Two
5.4
33,35,36,39
Enthalpy
1
Three
5.5
34,40, 45, 49,
51, 52, 54
Calorimetry
2
Make sure to read
p.183 Strategies in
Chemistry: Using
Enthalpy as a Guide
Day Four
Five
5.6
8, 14, 46,
52,55, 56, 61,
62, 63
Six
Seven
3
Bomb calorimetry and
Hess Law
4
Hess Law Lab
5.7
65,66, 70, 72,
111
Eight
Assign practice
test
Nine
Review, 112
Ten
Calorimeter lab
Test
MC and
Written
Enthalpies of
formation
5
Review
video
Test problem(s) posted
online
Chapter Five: Thermochemistry Notes
Give It Some Thought on page 169
What are the terms for the energy an object possesses?
A) Because of it’s motion?
B)
Because of it’s Position?
What terms are used to describe changes associated with?
C) Temperature Changes?
D) Moving an Object?
System vs. Surroundings…
5.3 Determining the Sign of H (Pg 178)
1) Indicate the sign of the enthalpy change, H, in each of the following processes carried out under
atmospheric pressure, and indicate whether the process is endothermic or exothermic:
A) An ice cube melts.
B)
2)
1 g of butane (C4H10) is combusted in sufficient oxygen to give complete combustion to CO2
and H2O.
Suppose we combine 1 g of butane and sufficient oxygen to completely combust in a cylinder. The
cylinder is perfectly insulating, so not heat can escape to the surroundings. A spark initiates combustion
of the butane, which forms carbon dioxide and water vapor. If we used this apparatus to the measure the
enthalpy change in the reaction, would the piston rise, fall, or stay the same?
Thermochemical Equation…what is this?
Give It Some Thought on page 180
What information is summarized by the coefficients in a thermochemical equation?
5.4 Relating H to Quantities of Reactants and Products (Pg 182)
1) How much heat is released when 4.50 g of methane gas is burned in a constant-pressure system?
2)
Hydrogen peroxide can decompose to water and oxygen by the following reaction:
2H2O2(l)  2H2O(l) + O2(g)
H = -196 kJ
Calculate the value of q when 5.00g of H2O2(l) decompose at constant pressure.
Give It Some Thought on page 185
How are the energy changes of a system and its surroundings related?
How is the heat gained or lost by a system to the heat gain or lost by its surroundings?
PE 5.7 (Pg 187)
A 0.5865-g sample of lactic acid (HC3H5O3) is burned in a calorimeter whose heat capacity is 4.812 kJ/°C. The
temperature increased from 23.10°C to 24.95°C. Calculate the heat of the combustion of lactic acid (a) per gram and
(b) per mole.
Give It Some Thought on page 189
What effect do the following changes have on H for a reaction:
A) Reversing a reaction?
B) Multiplying coefficients by 2?
5.8 Example Problems for Modeling for Calorimetry and Hess’ Law (Pg 189)
How much energy is needed to warm 250g of water (about 1 cup) from 22˚C to near its boiling point, 98˚C? The
specific heat of water is 4.184 J/g˚C
What is the molar heat capacity of water?
When a student mixes 50mL of 1.0M HCl and 50mL of 1.0M NaOH in a coffee-cup calorimeter, the temperature of the
resultant solution increases from 21.0˚C to 27.5˚C. Calculate the enthalpy change for the reaction, assuming that the
calorimeter loses only a negligible quantity of heat, that the total volume of the solution is 100.0mL, that its density is
1.0g/mL, and that its specific heat is 4.184J/g˚C.
Large beds of rocks are used in some solar-heated homes to store heat. Assume that the specific heat of the rocks is
0.082 J/g-K. Calculate the quantity of heat absorbed by 50.0 kg of rocks if their temperature increases by 12.0˚C
What temperature change would these rocks undergo if they emitted 450 kJ of heat?
Methylhydrazine (CH6N2) is commonly used as a liquid rocket fuel. The combustion of methylhydrazine with oxygen
produces nitrogen, carbon dioxide and water.
2CH6N2 + 5O2  2N2 + 2CO2 + 6H2O
When 4.00g of methylhydrazine is combusted in a bomb calorimeter, the temperature of the calorimeter increases from
25.00˚C to 39.50˚C. In a separate experiment the heat capacity of the calorimeter is measured to be 7.794 kJ/˚C. What
is the heat of reaction for the combustion of a mole of CH6N2?
PE 5.8
Carbon occurs in two forms, graphite and diamond. The enthalpy of the combustion of the graphite is -393.5 kJ/mol
and that of diamond is -395.4 kJ/mol:
C(graphite) + O2(g) CO2(g) H1= -393.5 kJ
C(carbon) +O2(g)  CO2(g) H2= -395.4 kJ
Calculate H for the conversion of graphite to diamond:
C(graphite) C(diamond) H3= ?
PE 5.9 (Pg 191)
Calculate H for reaction: NO(g)+O(g) NO2(g)
Given the following information
NO(g)+O3(g) NO2(g) +O2(g) H= -198.9 kJ
O3(g) 3/2 O2(g)
H= -142.3 kJ
O2(g) 2 O(g)
H= 495.0 kJ
Given:
C(s) + O2(g)  CO2(g)
CO(g) + 1/2O2(g)  CO2(g)
H = -393.5kJ
H = -283.0kJ
Find:
C(s) + 1/2O2(g)  CO(g)
Calculate H for the reaction: 2C(s) + H2(g)  C2H2(g)
Given the following reactions and their respective enthalpy changes:
C2H2(g) + 5/2O2(g)  2CO2 + H2O
C(s) + O2(g)  CO2(g)
H2(g) + 1/2O2(g)  H2O
H = -1299.6kJ
H = -393.5kJ
H = -285.8kJ
Give it some thought:
In table 5.3 (page 192), the standard enthalpy of formation of C2H2(g) is listed as 226.7 kJ/mol. Write the
thermochemical equation associated with Hf for this substance.
Sample exercise 5.10
For which of the following reactions at 25°C would the enthalpy change represent a standard enthalpy of
formation? For those where it does not, what changes would need to be made in the reaction conditions?
(a) 2 Na(s) + ½ O2(g) Na2O(s)
(b) 2K(l) + Cl2(g) 2KCl(s)
(c) C6H12O6(s) 6C(Diamond) + 6H2(g) + 3O2(g)
PE 5.10 (Pg 193)
Write the equation corresponding to the standard enthalpy of formation of liquid carbon tetrachloride (CCl4).
Sample exercise
(a) calculate the standard enthalpy change for the combustion of 1 mol of benzene, C6H6(l), to CO2(g) and H2O(l).
(b) compare the quantity of heat produced by combustion of 1.00 g propane to that produced by 1.00 g benzene.
PE 5.12 (Pg 195)
Using the standard enthalpies of formation listed in table 5.3, calculate the enthalpy change for the combustion of 1 mol
of ethanol:
C2H2OH(l) + 3O2(g) 2CO2(g) +3H2O(l)
Sample exercise
The standard enthalpy change for the reaction
CaCO3(s) CaO(s) +CO2(g)
is 178.1 kJ. From the values for the standard enthalpies of formation of CaO(s) and CO2(g) given in table 5.3, calculate
the standard enthalpy of formation of CaCO3(s).
PE 5.12 (Pg 196)
Given the following standard enthalpy change, use the standard enthalpies of formation in table 5.3 to calculate the
standard enthalpy of formation of CuO(s):
CuO(s) + H2(g) Cu(s) +H2O(l) H= -129.7 kJ
Some Extra Sample Problems:
When 50.0 mL of .100 M AgNO3 and 50.0 mL of 0.100 M HCl are mixed in a constant-pressure calorimeter, the
temperature of the mixture increases from 22.20˚C to 23.01˚C. The temperature increase is caused by the following
reaction:
AgNO3(aq) + HCl(aq)  AgCl(s) + HNO3(aq)
Calculate H for this reaction in kJ/mol AgNO3, assuming that the combined solution has a mass of 100 g
and a specific heat of 4.18J/g-˚C
A 0.5865-g sample of lactic acid (HC3H5O3) is burned in a calorimeter whose heat capacity is 4.812 kJ/˚C. The
temperature increases from 23.10˚C to 24.95˚C. Calculated the heat of combustion of lactic acid (a) per gram and (b)
per mole.
You try:
Calculate H for the reaction NO(g) + O(g)  NO2(g) given:
NO(g) + O3(g)  NO2(g) + O2(g) H = -198.9kJ
O3(g)  3/2O2(g)
H = -142.3kJ
O2(g)  2O(g)
H = 495.0kJ