Name:    Practice Test #8 - Thermochemistry

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.

1.

Which one of the following statements is INCORRECT?
 a. Energy is neither created nor destroyed in chemical reactions. b. Kinetic energy is the energy associated with motion. c. Exothermic processes transfer heat from the surrounding into the system. d. Increasing the thermal energy of a gas increases the motion of its atoms. e. Energy is the capacity to do work.

2.

How many nutritional calories are equivalent to 875 kJ?
 a. 0.875 Cal b. 209 Cal c. 3.66 x 103 Cal d. 2.09 x 105 Cal e. 3.66 x 106 Cal

3.

If 1.00 mole of ethanol, CH3CH2OH, at 22.0 °C absorbs 1.45 kJ of heat, what is the final temperature of the ethanol? The specific heat capacity of ethanol is 2.44 J/g·K.
 a. 9.1 °C b. 22.0 °C c. 34.9 °C d. 47.0 °C e. 616 °C

4.

How much energy is required to change the temperature of 21.5 g Cu from 27.0 °C to 88.1 °C? The specific heat capacity of copper is 0.385 J/g·K.
 a. 223 J b. 506 J c. 641 J d. 729 J e. 3.41 ´ 103 J

5.

If 50.0 g H2O at 13.6 °C is combined with 85.0 g H2O at 93.7 °C, what is the final temperature of the mixture? The specific heat capacity of water is 4.184 J/g·K.
 a. 26.1 °C b. 40.0 °C c. 56.1 °C d. 64.0 °C e. 80.1 °C

6.

If 46.1 g Zn at 18.0 °C is placed in 80.0 g H2O at 75.0 °C, what is the final temperature of the mixture? The specific heat capacities of zinc and water are 0.388 J/g·K and 4.184 J/g·K, respectively.
 a. 20.9 °C b. 27.3 °C c. 64.5 °C d. 65.7 °C e. 72.1 °C

7.

When 27.0 g of an unknown metal at 88.4 °C is placed in 115 g H2O at 21.0 °C, the final temperature of the water is 23.7 °C. What is the specific heat capacity of the metal? The specific heat capacity of water is 4.184 J/g·K.
 a. 0.34 J/g·K b. 0.51 J/g·K c. 0.74 J/g·K d. 0.94J/g·K e. 1.4 J/g·K

8.

Calculate the amount of heat required to change 50.0 g ice at -20.0 °C to steam at 135 °C. (Heat of fusion = 333 J/g; heat of vaporization = 2260 J/g; specific heat capacities: ice = 2.09 J/g·K, liquid water = 4.18 J/g·K, steam = 1.84 J/g·K)
 a. 4.18 kJ b. 32.4 kJ c. 78.8 kJ d. 135 kJ e. 156 kJ

9.

The heat of vaporization of benzene, C6H6, is 30.8 kJ/mol at its boiling point of 80.1 °C. How much heat is required to vaporize 128 g benzene at its boiling point?
 a. 4.04 kJ b. 18.8 kJ c. 19.3 kJ d. 50.5 kJ e. 4.04 ´ 103 kJ

10.

Calculate DE for the system in which a gas absorbs 31 J of heat and does 18 J of work on the surroundings?
 a. -49 J b. -13 J c. +13 J d. +31 J e. +49 J

11.

The thermochemical equation for the combustion of butane is shown below.
C4H10(g) + 13/2 O2(g) 4 CO2(g) + 5 H2O(l) ) DH° = -2877 kJ
What is the enthalpy change for the following reaction?
16 CO2(g) + 20 H2O(l) 4 C4H10(g) + 26 O2(g)
 a. -5754 kJ b. -719.2 kJ c. +719.2 kJ d. +5754 kJ e. +1.151 ´ 104 kJ

12.

Hydrazine, N2H4, is a liquid used as a rocket fuel. It reacts with oxygen to yield nitrogen gas and water.
N2H4(l) + O2(g) N2(g) + 2 H2O(l)
The reaction of 3.80 g N2H4 evolves 73.7 kJ of heat. Calculate the enthalpy change per mole of hydrazine combusted.
 a. -8.74 kJ/mol b. -19.4 kJ/mol c. -2.80 x 102 kJ/mol d. -622 kJ/mol e. -8.98 x 103 kJ/mol

13.

The molar enthalpy of combustion for glucose, C6H12O6, is -2803 kJ. A mass of 1.150 g glucose is combusted in a bomb calorimeter. If the calorimeter contains 925 g H2O and the bomb has a heat capacity of 622 J/K, what is the temperature increase of the bomb calorimeter? The specific heat capacity of water is 4.184 J/g·K and the molar mass of glucose is 180.2 g/mol.
 a. 0.72 K b. 2.76 K c. 3.98 K d. 5.12 K e. 7.20 K

14.

Determine the heat of vaporization of titanium(IV) chloride given the enthalpies of reaction below.

Ti(s) + 2 Cl2(g) TiCl4(l) DH = -804.2 kJ

Ti(s) + 2 Cl2(g) TiCl4(g) DH = -763.2 kJ
 a. -1567.4 kJ b. -41.0 kJ c. +1.054 kJ d. +41.0 kJ e. +1567.4 kJ

15.

Determine the heat of reaction for the oxidation of iron,
4 Fe(s) + 3 O2(g) ® 2 Fe2O3(s)

given the thermochemical equations below.
2 Fe(s) + 6 H2O(l) 2 Fe(OH)3(s) + 3 H2(g) DH = +321.8 kJ
2 H2O(l) 2 H2(g) + O2(g) DH = +571.7 kJ
Fe2O3(s) + 3 H2O(l) 2 Fe(OH)3(s) DH = +288.6 kJ
 a. -1648.7 kJ b. -1182.1 kJ c. -505.3 kJ d. +360.5 kJ e. +1447.1 kJ

16.

Calculate DH for the following reaction,
CaO(s) + CO2(g) CaCO3(s)
given the thermochemical equations below.
2 Ca(s) + O2(g) 2 CaO(s) DH = -1270.2 kJ
C(s) + O2(g) CO2(g) DH = -393.5 kJ
2 Ca(s) + 2 C(s) + 3 O2(g) 2 CaCO3(s) DH = -2413.8 kJ
 a. -4077.3 kJ b. -750.1 kJ c. -178.3 kJ d. +350.2 kJ e. +2870.6 kJ

17.

Calculate for sulfur dioxide,
S(s) + O2(g) SO2(g)
given the thermochemical equations below.
2 S(s) + 3 O2(g) 2 SO3(g) DH° = -791.5 kJ
2 SO2(g) + O2(g) 2 SO3(g) DH° = -197.9 kJ
 a. -296.8 kJ/mol b. -395.7 kJ/mol c. -494.7 kJ/mol d. -593.6 kJ/mol e. -989.4 kJ/mol

18.

Which of the following chemical equations corresponds to the standard molar enthalpy of formation of N2O?
 a. NO(g) + 1/2 N2(g) → N2O(g) b. N2(g) + 1/2 O2(g) → N2O(g) c. 2N(g) + O(g) → N2O(g) d. N2(g) + O(g) → N2O(g) e. 2 N2(g) + O2(g) → 2 N2O(g)

19.

Calculate for the combustion of gaseous ethanol,
C2H5OH(g) + 3 O2(g) 2 CO2(g) + 3 H2O(g)
using standard molar enthalpies of formation.

 molecule (kJ/mol) C2H5OH(g) -235.3 CO2(g) -393.5 H2O(g) -241.8
 a. -1747.7 kJ b. -1277.1 kJ c. -793.5 kJ d. -400.0 kJ e. -83.6 kJ

20.

The standard molar enthalpy of formation of NH3(g) is -45.9 kJ/mol. What is the enthalpy change if 5.38 g N2(s) and 3.32 g H2(g) react to produce NH3(g)?
 a. -75.6 kJ b. -50.4 kJ c. -17.6 kJ d. -8.81 kJ e. -1.20 kJ