Chapter 6
Thermochemistry
Section A
Question 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
Question 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) ΔHorxn = -198 kJ
A) 5.04 x 10-2 kJ
B) 9.9 x 102 kJ
C) 207 kJ
D) 5.0 x 102 kJ
E) None of the above
Question 3
The specific heat of aluminum is 0.214 cal/g·oC. Determine the energy, in calories, necessary to raise the temperature of a 55.5 g piece of aluminum
from 23.0 to 48.6oC.
A) 109 cal
B) 273 cal
C) 577 cal
D) 347 cal
E) 304 cal
Question 4
A 60.0 g sample of an alloy was heated to 96.00oC and then dropped into a beaker containing 87.0 g of water at a temperature of 24.10oC. The
temperature of the water rose to a final temperature of 27.63oC. The specific heat of water is 4.184 J/g·oC. What is the specific heat 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
Question 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 26.87oC. 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
Question 6
To which one of the following reactions, occurring at 25 oC, does the symbol ΔHof [H2SO4(l)] refer?
A) H2(g) + S(s) + 2 O2(g) ----> H2SO4(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)
Question 7
Given: SO2(g) + ½O2(g) ----> SO3(g) ΔHorxn = -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
Question 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) ΔHof = -1411 kJ;
C(s) + O2(g) ----> CO2(g) ΔHof = -393.5 kJ;
H2(g) + ½O2(g) ----> H2O(l) ΔHof = -285.8 kJ
A) 731 kJ
B) 2.77 x 103 kJ
C) 1.41 x 103 kJ
D) 87 kJ
E) 52 kJ
Question 9
Calculate ΔHorxn for the combustion reaction of CH4 shown below given the following:
ΔHof CH4(g) = -74.8 kJ/mol;
ΔHof CO2(g) = -393.5 kJ/mol;
ΔHof 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
Question 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
Question 11
Which of the following is incorrectly matched?
A) Radiant energy; solar energy able to influence global climate patterns
B) Thermal energy; related to temperature irrespective of the volume
C) Energy; capacity to do work
D) Chemical energy; potential energy
Question 12
Energy is the ability to do work and can be:
A) converted to one form to another
B) can be created and destroyed
C) used within a system without consequences
D) none of the above
Question 13
Standard enthalpy of reactions can be calculated from standard enthalpies of formation of reactants.
A) True
B) False
Question 14
In the equation ΔE is equal to q+w, which sign is correctly associated?
A) q; - exothermic
B) q; + endothermic
C) w; + by system on surrounding
D) w; + on system by surroundings
Section B
Question 1
An endothermic process
A) raises the temperature of one gram of a substance by one degree Celcius.
B) takes in heat from the surroundings.
C) increases the acidity of the surroundings.
D) gives off heat to the surroundings.
E) releases carbon dioxide into the surroundings.
Question 2
The chemical equation describing the conversion of SO2 into SO3 is shown below. Calculate Ho when 89.6 g of SO2 is converted into SO 3.
SO2(g) + ½O2(g) ----> SO3(g) Horxn = -99.1 kJ
A) -69.3 kJ
B) -139 kJ
C) 69.3 kJ
D) 139 kJ
E) -111 kJ
Question 3
How much energy in calories is required to heat 25.0 g of platinum (specific heat capacity = 0.032 cal/g.K) from 24.5 oC to 75.0 oC?
A) 48 cal
B) 20. cal
C) 80 cal
D) 40. cal
E) None of the above.
Question 4
If a substance has a specific heat capacity of 1.0 J/g·oC and a density of 2.0 g/mL, how much energy would be required to raise the temperature of
100 mL of the substance from 25 to 45 oC?
A) 0.20 kJ
B) 2.0 kJ
C) 4 kJ
D) 8 kJ
Question 5
A 0.468-g sample of pentane (C5H12) was burned in a bomb calorimeter. The temperature of the calorimeter and the 1.00 kg of water rose from
20.45 to 23.65 oC. The specific heat capacity of the calorimeter is 2.21 kJ/ oC, and the specific heat capacity of water is 4.184 J/g·oC. What is the
heat of combustion of one mole of C5 H12?
A) -7.07 x 103 kJ/mol
B) -2.05 kJ/mol
C) -3.16 x 103kJ/mol
D) 1.34 x 104 kJ/mol
E) 3.16 x 103 kJ/mol
Question 6
Calculate the standard heat of formation of carbon disulfide (CS2) from its elements, C(s) + 2 S(s) ----> CS2(l), given that:
C(s) + O2(g) ----> CO2(g), H = -393.5 kJ;
S(s) + O2(g) ----> SO2(g), H = -296.8 kJ; and
CS2(l) + 3 O2(g) ----> CO2(g) + 2 SO2(g), H = -1076.8 kJ.
A) -1767.1 kJ
B) -386.5 kJ
C) 89.7 kJ
D) 386.5 kJ
E) None of the above
Question 7
For which of the substances below is Hof = 0?
A) O2(g)
B) N2(l)
C) Na(g)
D) Xe(l)
E) A and B
Question 8
To which of the following reactions occurring a 25 oC does the symbol Hof [H2O(l)] apply?
A) H2O(l) ----> 2 H(g) + O(g)
B) 2 H(g) + O(g) ----> H2O(l)
C) H2(l) + ½O2(l) ----> H2O(l)
D) H2(g) + ½O2(g) ----> H2O(l)
E) H2O(g) ----> H2O(l)
Question 9
The heat of solution of KCl is 17.2 kJ/mol, and the combined heats of hydration of one mole of gaseous chloride ions and one mole of gaseous
potassium ions is -698 kJ. What is the lattice energy of potassium chloride?
A) -681 kJ/mol
B) 715 kJ/mol
C) -715 kJ/mol
D) -332 kJ/mol
E) 681 kJ/mol
Question 10
A certain gas expands in volume from 2.0 L to 24.5 L at constant temperature. Calculate the work done by the gas if it expands against a constant
pressure of 5 atm.
A) -112.5 J
B) 1.24 x 104 J
C) -1.14 x 104 J
D) 113 J
E) 1.14 x 104 J