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Chemistry, 7/e
Raymond Chang, Williams College

Thermochemistry

Self Assessment A



1

An exothermic reaction causes the surroundings to:
A)become basic.
B)decrease in temperature.
C)condense.
D)increase in temperature.
E)decrease in pressure.
2

How much heat is evolved when 320 g of SO2 is burned according to the chemical equation shown below? 2 SO2(g) + O2(g) ----> 2 SO3(g) DHorxn = -198 kJ
A)5.04 x 10-2 kJ
B)9.90 x 102 kJ
C)207 kJ
D)495 kJ
E)None of the above.
3

The specific heat of aluminum is 0.214 cal/g·oC. Determine the number of calories necessary to raise the temperature of a 55.5 g piece of aluminum from 23.0 to 48.6 oC.
A)109 cal
B)273 cal
C)577 cal
D)347 cal
E)304 cal
4

A 60.0 g sample of an alloy was heated to 96.00 oC and then dropped into a beaker containing 87.0 g of water at a temperature of 24.10 oC. The temperature of the water rose to a final temperature of 27.63 oC. The specific heat of water is 4.184 J/g·oC. What is the specific heat capacity of the alloy?
A)0.313 J/g·oC
B)2.16 J/g·oC
C)0.118 J/g·oC
D)1.72 J/g·oC
E)None of the above.
5

When 1.535 g of methanol (CH3OH) was burned in a constant-volume bomb calorimeter, the water temperature rose from 20.27 oC to 26.87 oC. If the mass of water surrounding the calorimeter was exactly 1000 g and the heat capacity of the bomb calorimeter was 1.75 kJ/oC, calculate the molar heat of combustion of CH3OH. The specific heat of water is 4.184 J/g·oC.
A)-8.17 x 105 kJ/mol
B)-817 kJ/mol
C)1.88 kJ/mol
D)817 kJ/mol
E)None of the above.
6

To which one of the following reactions, occurring at 25 oC, does the symbol DHof [H2SO4(l)] refer?
A)H2(g) + S(s) + 2 O2(g) ----> H2SO 4(l)
B)H2SO4(l) ----> H2(g) + S(s) + 2 O2(g)
C)H2(g) + S(g) + 2 O2(g) ----> H2SO4(l)
D)H2SO4(l) ----> 2 H(g) + S(s) + 4 O(g)
E)2 H(g) + S(g) + 4 O(g) ----> H2SO4(l)
7

Given: SO2(g) + ½O2(g) ----> SO3(g) DHorxn = -99 kJ, what is the enthalpy change for the following reaction? 2 SO3(g) ----> O2(g) + 2 SO2(g)
A)99 kJ
B)-99 kJ
C)49.5 kJ
D)-198 kJ
E)198 kJ
8

Find the standard enthalpy of formation of ethylene, C2H4(g), given the following data: C2H4(g) + 3 O2(g) ----> 2 CO2(g) + 2 H2O(l) DHof = -1411 kJ; C(s) + O2(g) ----> CO2(g) DHof = -393.5 kJ; H2(g) + ½O2(g) ----> H2O(l) DHof = -285.8 kJ
A)731 kJ
B)2.77 x 103 kJ
C)1.41 x 103 kJ
D)87 kJ
E)52 kJ
9

Calculate DHorxn for the combustion reaction of CH4 shown below given the following: DHof CH4(g) = -74.8 kJ/mol; DHof CO2(g) = -393.5 kJ/mol; and DHof H2O(l) = -285.5 kJ/mol. CH4(g) + 2 O2(g) ----> CO2(g) + 2 H2O(l)
A)-604.2 kJ
B)889.7 kJ
C)-997.7 kJ
D)-889.7 kJ
E)None of the above
10

A 1.300 g sample of benzoic acid (C7H6O2) was burned in a bomb calorimeter. The heat capacity of the entire apparatus, including the bomb, pail, thermometer, and water, was found to be 11,145 J/K. As a result of the reaction, the temperature of the calorimeter and water increased 4.627 K. What is the molar heat of combustion of benzoic acid?
A)4.84 x 106 kJ/mol
B)-2.96 kJ/mol
C)-4844 kJ/mol
D)549.1 kJ/mol
E)51.57 kJ/mol