Chapter 06 – Thermochemistry
77.
A gas is allowed to expand, at constant temperature, from a volume of 1.0 L to 10.1 L against an external pressure of 0.50
atm. If the gas absorbs 250 J of heat from the surroundings, what are the values of q, w, and E?
78. Which of the following processes always results in an increase in the energy of a system?
Chapter 06 – Thermochemistry
79.
For which of these reactions will the difference between H and E be the greatest?
80.
For which of these reactions will the difference between H and E be the smallest?
Chapter 06 – Thermochemistry
81.
At 25C, the following heats of reaction are known:
At the same temperature, use the above data to calculate the heat released (kJ) when 3.40 moles of ClF(g) reacts with excess
F2:
ClF(g) + F2(g) → ClF3(g)
Chapter 06 – Thermochemistry
82.
The bond enthalpy of the Br–Cl bond is equal to H for the reaction
BrCl(g) → Br(g) + Cl(g).
Use the following data to find the bond enthalpy of the Br–Cl bond.
83. The heat of solution of ammonium nitrate is 26.2 kJ/mol. If a 5.368 g sample of NH4NO3
is added to 40.0 mL of water in a calorimeter at 23.5C, what is the minimum temperature
reached by the solution? (The specific heat of water = 4.18 J/g·C; the heat capacity of the
calorimeter = 650. J/C.)
Chapter 06 – Thermochemistry
84. The heat of solution of ammonium chloride is 15.2 kJ/mol. If a 6.134 g sample of NH4Cl
is added to 65.0 mL of water in a calorimeter at 24.5C, what is the minimum temperature
reached by the solution? (The specific heat of water = 4.18 J/g·C; the heat capacity of the
calorimeter = 365. J/C.)
85.
Aluminum oxide can be reduced to aluminum metal using carbon, the other reaction product being carbon monoxide.
Determine the enthalpy change when 12.5 g of aluminum is produced by this method. [Hf(carbon monoxide) = –110.5
kJ/mol; Hf(aluminum oxide) = –1669.8 kJ/mol]
Chapter 06 – Thermochemistry
86.
Ozone (O3) in the atmosphere can be converted to oxygen gas by reaction with nitric oxide (NO). Nitrogen dioxide is also
produced in the reaction. What is the enthalpy change when 8.50L of ozone at a pressure of 1.00 atm and 25C reacts with
12.00 L of nitric oxide at the same initial pressure and temperature? [Hf(NO) = 90.4 kJ/mol; Hf(NO2) = 33.85 kJ/mol;
Hf(O3) = 142.2 kJ/mol]
87. Select True or False: Specific heat is defined as the amount of heat required to raise the
temperature of one gram of a substance by one degree Celsius.
Chapter 06 – Thermochemistry
88.
How many grams of ethylene (C2H4) would have to be burned to produce 450 kJ of heat?
C2H4(g) + 3O2(g) → 2CO2(g) + H2O(l) Hrxn = –1411 kJ/mol
89.
Calculate the enthalpy of reaction for H2(g) + C2H4(g) → C2H6(g).
[Hf(C2H4(g)) = 52.3 kJ/mol; Hf(C2H6(g)) = –84.7 kJ/mol]
Chapter 06 – Thermochemistry
90.
The enthalpy of combustion of acetylene C2H2 is described by
C2H2(g) + (5/2)O2(g) → 2CO2(g) + H2O(l), Hrxn= –1299 kJ/mol.
Calculate the enthalpy of formation of acetylene, given the following enthalpies of formation
Hf[CO2(g)] = –393.5 kJ/mol
Hf[H2O(l)] = –285.8 kJ/mol
91.
Given the following H values,
H2(g) + O2(g) → H2O(l) Hf = –285.8 kJ/mol
H2O2(l) → H2(g) + O2(g) Hrxn = 187.6 kJ/mol
calculate Hrxn for the reaction H2O2(l) → H2O(l) + O2(g).
Chapter 06 – Thermochemistry
92. The heat of solution of calcium chloride CaCl2 is –82.8 kJ/mol, and the combined heats of
hydration of 1.00 mole of gaseous calcium ions and 2.00 mole of gaseous chloride ions is –
2327 kJ. What is the lattice energy of calcium chloride?
93. Select True or False: The heat of solution of NH4NO3 is 26.2 kJ/mol. Heat is evolved
when a solution of NH4NO3 is diluted by addition of more water.
Chapter 06 – Thermochemistry
94. A 26.2 g piece of copper metal is heated from 21.5C to 201.6C. Calculate the amount of
heat absorbed by the metal. The specific heat of Cu is 0.385 J/g·C.
95. A 0.1946 g piece of magnesium metal is burned in a constant-volume calorimeter that has
a heat capacity of 1349 J/C. The calorimeter contains 500. g of water and the temperature
rise is 1.40C. Calculate the heat of combustion of magnesium metal in kJ/g, given that the
specific heat of water = 4.184 J/g·C.
Chapter 06 – Thermochemistry
96. A 0.3423 g sample of pentane, C5H12, was burned in a bomb calorimeter. The temperature
of the calorimeter and the 1.000 kg of water contained therein rose from 20.22C to 22.82C.
The heat capacity of the calorimeter is 2.21 kJ/C. The heat capacity of water = 4.184 J/g·C.
How much heat was given off during combustion of the sample of pentane?
97. A 0.3423 g sample of pentane, C5H12, was burned in a bomb calorimeter. The temperature
of the calorimeter and the 1.000 kg of water contained therein rose from 20.22C to 22.82C.
The heat capacity of the calorimeter is 2.21 kJ/C. The heat capacity of water = 4.184 J/g·C.
What is the heat of combustion, in kilojoules, per gram of pentane?