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AP Chemistry Unit 6: Thermodynamics

12 questions

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Unit 6: Thermodynamics

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Question 1

Which of the following thermochemical properties can be calculated from a Born-Haber cycle?

A.Rate constant of an ionic reactionB.Lattice energy of an ionic compoundC.Equilibrium constant for a dissolution reactionD.Bond order of an ionic compound

Question 2

In a bomb calorimeter experiment, $1.00 g$ of glucose ( $M = 180 g/mol$ ) causes a temperature rise of $2.00° C$ in a calorimeter with heat capacity $C_{cal} = 7.78 kJ/°C$ . What is the molar heat of combustion of glucose?

- 15.6 kJ/g

- 2800 kJ/mol

- 5330 kJ/mol

- 156 kJ/mol

Question 3

Using the following standard enthalpies of formation, calculate $Δ H^{\circ}$ for $C H_{4} (g) + 2 O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (l)$ :

$Δ H_{f}^{\circ} [C H_{4} (g)] = - 74.8 kJ/mol$

$Δ H_{f}^{\circ} [C O_{2} (g)] = - 393.5 kJ/mol$

$Δ H_{f}^{\circ} [H_{2} O (l)] = - 285.8 kJ/mol$

- 604.5 kJ/mol

- 890.3 kJ/mol

+ 890.3 kJ/mol

- 965.1 kJ/mol

Question 4

At $25° C$ , the enthalpy of combustion of hydrogen is $- 241.8 kJ/mol$ (as gas) when $H_{2} O$ is formed as a vapor. The enthalpy of vaporization of water is $44.0 kJ/mol$ . What is the enthalpy of combustion when liquid water is formed?

- 197.8 kJ/mol

- 285.8 kJ/mol

- 241.8 kJ/mol

+ 44.0 kJ/mol

Question 5

When a hot metal block is placed in cool water and the system reaches thermal equilibrium, which statement is correct?

A.Heat flows from the water to the metal until their temperatures equalize.B.The heat lost by the metal equals the heat gained by the water (assuming no heat loss to surroundings).C.The metal loses more heat than the water gains because metal is denser.D.The temperature changes of the metal and water must be equal.

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Question 6

Which of the following best describes an endothermic reaction?

A.Products have lower potential energy than reactants;

Δ H < 0

.B.The system absorbs heat from the surroundings;

Δ H > 0

.C.The reaction releases energy as light.D.Temperature of the surroundings increases during the reaction.

Question 7

The average bond enthalpy of an O=O double bond is $498 kJ/mol$ and that of an O–H bond is $464 kJ/mol$ . Using bond enthalpies, estimate $Δ H$ for:

$2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (g)$

( $D (H - H) = 436 kJ/mol$ )

- 478 kJ

- 484 kJ

+ 484 kJ

- 928 kJ

Question 8

What is the difference between heat ( $q$ ) and temperature ( $T$ )?

A.Heat and temperature are the same thing measured in different units.B.Temperature measures the average kinetic energy of particles; heat is the energy transferred due to a temperature difference.C.Heat is a property of objects; temperature is a form of energy.D.A large object always has more heat than a small object at the same temperature.

Question 9

A student burns $1.00 g$ of ethanol in a calorimeter containing $500 g$ of water. The temperature rises from $22.5° C$ to $35.7° C$ . What is the heat absorbed by the water? ( $c_{water} = 4.18 J/ (g \cdot °C)$ )

2.76 kJ

27.6 kJ

55.2 kJ

0.276 kJ

Question 10

Given:

(1) $C (s) + O_{2} (g) \to C O_{2} (g)$ , $Δ H_{1} = - 393.5 kJ$

(2) $2 CO (g) + O_{2} (g) \to 2 C O_{2} (g)$ , $Δ H_{2} = - 566.0 kJ$

Use Hess's Law to find $Δ H$ for: $2 C (s) + O_{2} (g) \to 2 CO (g)$

- 959.5 kJ

- 221.0 kJ

+ 221.0 kJ

- 172.5 kJ

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Question 11

The specific heat of aluminum is $0.900 J/ (g \cdot °C)$ and of water is $4.18 J/ (g \cdot °C)$ . Equal masses of aluminum and water absorb equal amounts of heat. Which statement is correct?

A.Aluminum undergoes a greater temperature increase.B.Water undergoes a greater temperature increase.C.Both undergo the same temperature increase.D.Water absorbs more total heat because it has a higher specific heat.

Question 12

A reaction at constant pressure releases $150 kJ$ of heat and does $30 kJ$ of work on the surroundings. What is $Δ H$ for this process?

- 120 kJ

- 180 kJ

- 150 kJ

+ 150 kJ

AP Chemistry Unit 6: Thermodynamics — Free with Answer Explanations | Test Practice Hub