Name:    Chapter 5 Online Practice Problems

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. The heat required to raise the temperature of 1.00 g H2O(l) by 1.00 °C is 1.00 J. b. 1.000 calories is equal to 4.184 J. c. 1.00 J is equal to 1.00 kg·m2·s-2. d. A dietary Calorie is equal to 1000 calories. e. 1000 calories is equal to 1 kcal.

2.

How many joules are equivalent to 235 calories?
 a. 0.0178 J b. 56.2 J c. 983 J d. 5.62 ´ 103 J e. 1.67 ´ 104 J

3.

Specific heat capacity is
 a. the quantity of heat needed to change 1.00 g of a substance by 1.00 K. b. the mass of a substance that 1.00 J of energy will heat by 1.00 K. c. the mass of a substance that 1.00 cal of energy will heat by 1.00 K. d. the temperature change undergone when 1.00 g of a substance absorbs 4.184 J. e. the quantity of heat required to melt 4.184 g of a substance.

4.

If 136 J is required to change the temperature of 8.75 g of nickel by 35.0 K, what is the specific heat capacity of mercury?
 a. 0.0294 J/g·K b. 0.311 J/g·K c. 0.417 J/g·K d. 0.444 J/g·K e. 2.25 J/g·K

5.

If the same amount of heat is added to 5.00 g samples of each of the metals below, which metal will experience the smallest temperature change?

 Metal Specific Heat Capacity (J/g·K) Al 0.897 Au 0.129 Cu 0.385 Fe 0.449 K 0.753
 a. Al b. Au c. Cu d. Fe e. K

6.

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

7.

Which of the following statements is CORRECT?
 a. If a reaction occurs at constant pressure, w = DE. b. If a reaction occurs at constant pressure, q = DH. c. If a reaction occurs at constant pressure, q = DE. d. If a reaction occurs at constant volume, DE > DH. e. If a reaction occurs at constant volume, w = DE.

8.

One statement of the first law of thermodynamics is that
 a. the amount of work done on a system is dependent of pathway. b. the total work done on a system must equal the heat absorbed by the system. c. the heat flow in or out of a system is independent of pathway. d. the total energy flow in or out of a system is equal to the sum of the heat transferred to or from the system and the work done by or on the system. e. in any chemical process the heat flow must equal the change in enthalpy.

9.

The thermochemical equation for the combustion of hexane is shown below.

C6H14(g) + 19/2 O2(g) ® 6 CO2(g) + 7 H2O(g) DH° = -4163 kJ

What is the enthalpy change for the combustion of 2.50 g C6H14?
 a. -121 kJ b. -1.66 ´ 103 kJ c. -1.04 ´ 104 kJ d. -1.43 ´ 105 kJ e. -3.59 ´ 105 kJ

10.

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 ´ 102 kJ/mol d. -622 kJ/mol e. -8.98 ´ 103 kJ/mol

11.

If 1.86 g MgO is combined with 100.0 mL of 1.00 M HCl (density 100.0 g/mL) in a coffee cup calorimeter, the temperature of the resulting solution increases from 21.3 °C to 35.7 °C. Calculate the enthalpy change for the reaction per mole of MgO. Assume that the specific heat capacity of the solution is 4.18 J/g·K.
 a. -6.13 kJ b. -28.3 kJ c. -133 kJ d. -329 kJ e. -613 kJ

12.

A 2.885 g sample of methanol, CH3OH, is combusted in a bomb calorimeter. The temperature of the calorimeter increases by 11.38 K. If the heat capacity of the bomb is 727.1 J/K and it contains 1.200 kg of water, what is the heat evolved per mole of methanol combusted? The specific heat capacity of water is 4.184 J/g·K and the molar mass of methanol is 32.04 g/mol.
 a. -65.41 kJ/mol b. -91.89 kJ/mol c. -634.5 kJ/mol d. -726.5 kJ/mol e. -1.019 ´ 106 kJ/mol

13.

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

14.

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

15.

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

16.

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

17.

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

18.

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.

19.

Which one of the following statements is INCORRECT?
 a. In an exothermic process heat is transferred from the system to the surroundings. b. The greater the heat capacity of an object, the more thermal energy it can store. c. The SI unit of specific heat capacity is joules per gram per Kelvin. d. The specific heat capacity has a positive value for liquids and a negative value for gases. e. When heat is transferred from the system to the surroundings, q is negative.

20.

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

21.

A chemical reaction in a bomb calorimeter evolves 5.17 kJ of heat. If the heat capacity of the calorimeter is 1.08 kJ/°C, what is the temperature change of the calorimeter?
 a. 0.209 °C b. 4.09 °C c. 4.79 °C d. 5.58 °C e. 6.25 °C

22.

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

23.

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)