Chapter 6 2 41 Styrene C8h8 One The Substances Used

Chapter 06 – Thermochemistry

41.

Styrene, C8H8, is one of the substances used in the production of synthetic rubber. When styrene burns in oxygen to form

carbon dioxide and liquid water under standard-state conditions at 25C, 42.62 kJ are released per gram of styrene. Find the

standard enthalpy of formation of styrene at 25C.

(Given: Hf[CO2(g)] = –393.5 kJ/mol, Hf[H2O(l)] = –285.8 kJ/mol, Hf[H2O(g)] = –241.8 kJ/mol)

42.

Given 2Al(s) + (3/2)O2(g) → Al2O3(s), Hf = –1,670 kJ/mol for Al2O3 (s).

Determine H for the reaction 2Al2O3(s) →4Al(s) + 3O2(g).

Chapter 06 – Thermochemistry

43.

Calculate the standard enthalpy of formation of liquid methanol, CH3OH(l), using the following information:

Chapter 06 – Thermochemistry

44.

Calculate the standard enthalpy change for the reaction

2C8H18(l) + 17O2(g) → 16CO(g) + 18H2O(l).

Given

Chapter 06 – Thermochemistry

45.

During volcanic eruptions, hydrogen sulfide gas is given off and oxidized by air according to the following chemical

equation:

2H2S(g) + 3O2(g) → 2SO2(g) + 2H2O(g)

Calculate the standard enthalpy change for the above reaction given:

46.

Calculate the standard enthalpy change for the reaction

2C8H18(l) + 21O2(g) → 8CO(g) + 8CO2(g) + 18H2O(l).

Given:

2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(l) H = –11,020 kJ/mol

2CO(g) + O2(g) → 2CO2(g) H = –566.0 kJ/mol

Chapter 06 – Thermochemistry

47.

Calculate the standard enthalpy change for the reaction

2A + 2A2 + 4AB + B → 5A2B

Given:

Chapter 06 – Thermochemistry

48.

Calculate the standard enthalpy change for the reaction

4A + 2B → 2AB + A2

Given:

Chapter 06 – Thermochemistry

49.

Calculate the heat required when 2.50 mol of A reacts with excess B and A2B according to the reaction:

2A + B + A2B → 2AB + A2

Given:

50.

How much heat (kJ) is evolved when 4.50 g of Fe2O3 is reacted with excess carbon monoxide using the equation below?

Fe2O3(s) + 3CO(g) → 2 Fe(s) + 3 CO2(g) Hrxn = – 24.8 kJ/mol,

Chapter 06 – Thermochemistry

51.

Given H2(g) + (1/2)O2(g) → H2O(l), H = –286 kJ/mol, determine the standard enthalpy change for the reaction 2H2O(l) →

2H2(g) + O2(g).

Chapter 06 – Thermochemistry

52.

Pentaborane B5H9(s) burns vigorously in O2 to give B2O3(s) and H2O(l). Calculate Hrxn for the combustion of 5.00 mol of

B5H9.

Hf[B2O3(s)] = –1,273.5 kJ/mol

Hf[B5H9(s)] = 73.2 kJ/mol

Hf[H2O(l)] = –285.8 kJ/mol

53.

Concerning the reaction

how many grams of C(graphite) must be burned to release 275 kJ of heat?

Chapter 06 – Thermochemistry

54.

The combustion of butane produces heat according to the equation

2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(l), Hrxn= –5,314 kJ/mol.

How many grams of butane must be burned to release 1.00  104 kJ of heat?

55.

The combustion of butane produces heat according to the equation

2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(l), Hrxn= –5,314 kJ/mol.

How many grams of CO2 are produced per 1.00  104 kJ of heat released?

Chapter 06 – Thermochemistry

56.

Given that CaO(s) + H2O(l) → Ca(OH)2(s), Hrxn = –64.8 kJ/mol, how many grams of CaO must react in order to liberate

525 kJ of heat?

57.

The combustion of pentane produces heat according to the equation

C5H12(l) + 8O2(g) → 5CO2(g) + 6H2O(l), Hrxn= –3,510 kJ/mol.

How many grams of CO2 are produced per 2.50  103 kJ of heat released?

Chapter 06 – Thermochemistry

58.

An average home in Colorado requires 20. GJ of heat per month. How many grams of natural gas (methane) must be burned

to supply this energy?

CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) Hrxn= –890.4 kJ/mol

59.

Given the thermochemical equation 2SO2(g) + O2(g) → 2SO3(g), Hrxn= –198 kJ/mol, how much heat is evolved when 600.

g of SO2 is burned?

Chapter 06 – Thermochemistry

60.

Determine the heat given off to the surroundings when 9.0 g of aluminum reacts according to the equation 2Al + Fe2O3 →

Al2O3 + 2Fe, Hrxn= –849 kJ/mol.

61.

Find the heat absorbed from the surroundings when 15 g of O2 reacts according to the equation O + O2 → O3, Hrxn= –103

kJ/mol.

Chapter 06 – Thermochemistry

62.

Ethanol (C2H5OH) burns according to the equation

C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l), Hrxn = –1367 kJ/mol.

How much heat is released when 35.0 g of ethanol is burned?

63.

Methanol (CH3OH) burns according to the equation

2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(l), Hrxn = –1454 kJ/mol.

How much heat, in kilojoules, is given off when 75.0 g of methanol is burned?

Chapter 06 – Thermochemistry

64.

Calcium oxide and water react in an exothermic reaction:

CaO(s) + H2O(l) → Ca(OH)2(s), Hrxn = –64.8 kJ/mol.

How much heat would be liberated when 7.15 g CaO(s) is dropped into a beaker containing 152g H2O?

65.

Solid sodium peroxide (Na2O2) reacts with liquid water yielding aqueous sodium hydroxide and oxygen gas. How much heat

is released when 250.0 L of oxygen gas is produced from the reaction of sodium peroxide and water if the reaction is carried

out in an open container at 1.000 atm pressure and 25C?

(Given: Hf[Na2O2(s)] = –510.9 kJ/mol; Hf[NaOH(aq)] = –469.2 kJ/mol; Hf[H2O(l)] = –285.8 kJ/mol)

Chapter 06 – Thermochemistry

66.

At 25C, the standard enthalpy of formation of anhydrous sodium carbonate is –1130.9 kJ/mol, whereas the standard

enthalpy of formation of sodium carbonate monohydrate is –1430.1 kJ/mol. Determine H at 25C for the reaction

Na2CO3(s) + H2O(l) → Na2CO3·H2O(s).

(Given: Hf[H2O(l)] = –285.8 kJ/mol)

67. According to the first law of thermodynamics:

Chapter 06 – Thermochemistry

68. The heat of solution of KCl is 17.2 kJ/mol and the lattice energy of KCl(s) is 701.2

kJ/mol. Calculate the total heat of hydration of 1.00 mol of gas phase K+ ions and Cl– ions.

69. The heat of solution of LiCl is –37.1 kJ/mol, and the lattice energy of LiCl(s) is 828

kJ/mol. Calculate the total heat of hydration of 1.00 mol of gas phase Li+ ions and Cl– ions.

70. The total heat of hydration of 1.00 mol of gas phase Li+ ions and Cl – ions is –865 kJ. The

lattice energy of LiCl(s) is 828 kJ/mol. Calculate the heat of solution of LiCl.

Chapter 06 – Thermochemistry

71.

10.1 g CaO is dropped into a styrofoam coffee cup containing 157 g H2O at 18.0C.

If the following reaction occurs, what temperature will the water reach, assuming that the cup is a perfect insulator and that

the cup absorbs only a negligible amount of heat? (The specific heat of water = 4.18 J/g· C)

CaO(s) + H2O(l) → Ca(OH)2(s) Hrxn = –64.8 kJ/mol

72. The enthalpy change when a strong acid is neutralized by strong base is –56.1 kJ/mol. If

135 mL of 0.450 M HI at 23.15C is mixed with 145 mL of 0.500 M NaOH, also at 23.15C,

what is the maximum temperature reached by the resulting solution? (Assume that there is no

heat loss to the container, that the specific heat of the final solution is 4.18 J/g·C, and that the

density of the final solution is that of water.)

Chapter 06 – Thermochemistry

73. The enthalpy change when a strong acid is neutralized by strong base is –56.1 kJ/mol. If

12.0 mL of 6.00 M HBr at 21.30C is mixed with 300. mL of 0.250 M NaOH, also at

21.30C, what is the maximum temperature reached by the resulting solution? (Assume that

there is no heat loss to the container, that the specific heat of the final solution is 4.18 J/g·C,

and that the density of the final solution is that of water.)

74. Calculate the amount of work done, in joules, when 2.5 mole of H2O vaporizes at 1.0 atm

and 25C. Assume the volume of liquid H2O is negligible compared to that of vapor. (1 L·atm

= 101.3 J)

Chapter 06 – Thermochemistry

75. A gas is compressed in a cylinder from a volume of 20.0 L to 2.0 L by a constant pressure

of 10.0 atm. Calculate the amount of work done on the system.

76. Calculate the amount of work done against an atmospheric pressure of 1.00 atm when

500.0 g of zinc dissolves in excess acid at 30.0C.

Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)