Rev. for Test on Ch. 6
AP Chem
Name
1. Phileas Fogg, the character who went around the world in 80 days, was very fussy about his bathwater temperature. It had
to be exactly 38.0o C. You are his butler, and one morning while checking his bath temperature, you notice that it’s 42.0 oC.
You plan to cool the 100.0 kg of water to the desired temperature by adding an aluminum-duckie originally at freezer
temperature (-24.0oC). Of what mass should the Al-duckie be? [Specific heat of Al = 0.900 J/(goC); density of water =1 .00
g/ml]. Assume that no heat is lost to the air.
2. A gas absorbs 45 kJ of heat and does 29kJ of work. Calculate ΔE.
3. What does it mean when:
a). q is negative
b). w is positive
4. The volume of a gas is decreased form 5.00 L to 5.00 mL at a constant pressure of 2.00 atm. Calculate the work (in
joules) associated with this process. ( 1 L-atm = 101.3 J)
5. Consider the following reaction:
2N2(g) + O2(g) --> 2N2O(g)
ΔΗ = +163.2 kJ
a). Is the reaction exothermic or endothermic?
b). Calculate the amount of heat transferred when 25.0 g of N 2O(g) forms by this reaction at constant pressure.
c). How many grams of nitrogen gas must react to produce an enthalpy change of 5.00 kJ?
d). How many kilojoules of heat are produced when 10.0 g of N 2O(g)is decomposed into N2(g) and O2(g) at constant
pressure?
6. When solutions containing silver ions and chloride ions are mixed, silver chloride precipitates:
Ag+(aq) + Cl-(aq) --> AgCl(s)
ΔΗ = -65.5 kJ
a). Calculate ΔΗ for formation of 0.500 mol of AgCl by this reaction.
b). Calculate ΔΗ for formation of 7.00 g of AgCl.
c). What would ΔΗ be for the reverse reaction of 1 mol of AgCl(s) dissolving in water?
7. Which of the following statements (a-c) are correct?
a) The internal energy (ΔE)of a system increases when more work is done by the system than heat was flowing into the
system.
b). The internal energy(ΔE) of a system decreases when work is done on the system and heat is flowing into the system.
c). The system does work on the surroundings when a gas expands against a constant external pressure.
d). all statements are true
e). all statements are false
8. The specific heat capacity of aluminum is 0.900 J/g oC.
a. Calculate the energy needed to raise the temperature of a 8.50 x 10 2 g block of aluminum from 22.8 oC to 94.6 oC.
b. Calculate the molar heat capacity of aluminum.
9. It takes 78.2 J to raise the temperature of 45.6 g of lead by 13.3 oC. Calculate the specific heat capacity of lead.
10. Given the following data:
S(s) + 3/2 O2(g) --> SO3(g) ΔHo = -395.3 kJ
2SO2(g) + O2(g) --> 2SO3(g)
ΔHo = -198.2 kJ
Calculate ΔHo for the reaction
S(s) + O2(g) --> SO2(g)
11. Given the following data:
H2(g) + 1/2 O2(g) --> H2O(l) ΔHo = -285.8 kJ
N2O5(g) + H2O(l) --> 2HNO3(l)
ΔHo = -76.6kJ
½ N2(g) + 3/2O2(g) + 1/2H2(g) --> HNO3(l) ΔHo = -174.1kJ
Calculate ΔHo for the reaction:
2N2(g) + 5O2(g) --> 2N2O5(g)
12. Use the values of ΔHfo given and in Appendix B to calculate ΔHo for the following reactions:
a. 4NH3(g) + 3O2(g) + 2CH4(g) --> 2HCN(g) + 6H2O(l)
(ΔHfo for HCN(g) = 135.1 kJ/mol)
b. NH3(g) + HCl(g) --> NH4Cl(s)
13. Calcium carbide, CaC2, reacts with water to form acetylene, C2H2 and Ca(OH)2. Form the following enthalpy of reaction
data and data in the Appendix B, calculate ΔHfo for CaC2(s). (Hint: set up the equation as products – reactants with x as the
value for CaC2 and set it equal to the ΔHo which equals -127.2 kJ.)
CaC2(s) + 2H2O(l) --> Ca(OH)2 (s) + C2H2 (g)
ΔHo = -127.2 kJ
Answers to selected problems:
1. mAl = 30036 g = 30.0 kg.
2.16 kJ
4. 1013 J
5. a. endothermic b. 46.3 kJ c. 1.72 g N 2 -18.5 kJ
6. a. –32.8 kJ b. –3.20 kJ c. 65.5 kJ
7. c
8. a. 54.9 kJ b. 24.3 J/mol oC
9. 0.129 J/g oC
10. –296.1 kJ
11. 28.4 kJ
12. a. –1110 kJ b. –177 kJ
13. ΔHfo for CaC2 = -61.2 kJ