Q: Calculate the standard enthalpy change ($$\Delta H^\circ) $$for the combustion of 1 mole of benzene ($$\mathrm{C_6H_6(l)}) $$given: $$\Delta H_f^\circ(\mathrm{CO_2$(g)}) = -393.5\ \text{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{H_2O(l)}) = -285.8\ \text{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{C_6H_6(l)}) = 49.0\ \text{kJ/mol}$$ for the reaction $$\mathrm{C_6H_6(l) + \frac{15}{2} O_2$(g) \rightarrow 6 CO_2$(g) + 3 H_2O(l)}.$$

$$\Delta H^\circ = -3267\ \text{kJ}$$

Q: Which of the following is the correct relationship for calculating the standard reaction entropy ($$\Delta S^\circ$$)?

$$\Delta S^\circ = \sum n S^\circ(\text{products}) - \sum n S^\circ(\text{reactants})$$

Question 1

Which of the following best describes an isolated system in thermodynamics?

Accepted Answer

A system that cannot exchange either energy or matter with its surroundings.

Question 2

A gas expands from 10.0 L to 20.0 L against a constant external pressure of 2.00 atm. What is the work done by the gas? ($$1\ 	ext{L} \cdot 	ext{atm} = 101.3\ 	ext{J})$$

Accepted Answer

$$w = -2026\ 	ext{J}$$

Question 3

Which equation correctly relates the change in internal energy ($$\Delta U) to $$heat ($$q) $$and work ($$w$$)?

Accepted Answer

$$\Delta U = q + w$$

Question 4

A 50.0 g sample of water at $$100^\circC is $$mixed with 82.0 g of water at $$65.0^\circC. $$What is the final temperature of the mixture? ($$C_s = 4.184\ 	ext{J/g} \cdot ^\circ	ext{C})$$

Accepted Answer

$$T_f = 84.2^\circ	ext{C}$$

Question 5

Which of the following statements about exothermic and endothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat to the surroundings.

Question 6

Calculate the standard enthalpy change ($$\Delta H^\circ) $$for the combustion of 1 mole of benzene ($$\mathrm{C_6H_6(l)}) $$given: $$\Delta H_f^\circ(\mathrm{CO_2$(g)}) = -393.5\ 	ext{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{H_2O(l)}) = -285.8\ 	ext{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{C_6H_6(l)}) = 49.0\ 	ext{kJ/mol}$$ for the reaction $$\mathrm{C_6H_6(l) + \frac{15}{2} O_2$(g) ightarrow 6 CO_2$(g) + 3 H_2O(l)}.$$

Accepted Answer

$$\Delta H^\circ = -3267\ 	ext{kJ}$$

Question 7

Which of the following best describes entropy ($$S$$)?

Accepted Answer

A measure of the disorder or randomness of a system.

Question 8

For the process $$\mathrm{H_2O(l) \rightarrow H_2O(g)} at 1 $$atm, which of the following is true about the entropy change ($$\Delta S$$)?

Accepted Answer

$$\Delta S \u003e 0$$

Question 9

Which equation gives the entropy change for a reversible phase transition at constant temperature?

Accepted Answer

$$\Delta S = \frac{\Delta H}{T}$$

Question 10

A reaction has $$\Delta H = +100\ 	ext{kJ}$$ and $$\Delta S = +200\ 	ext{J/K}. At $$what temperature does the reaction become spontaneous?

Accepted Answer

$$T \u003e 500\ 	ext{K}$$

Question 11

Which of the following is the correct expression for the Gibbs free energy change ($$\Delta G) at $$constant temperature and pressure?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 12

Which of the following statements about the spontaneity of a process is correct?

Accepted Answer

A process is spontaneous if $$\Delta G \u003c 0.$$

Question 13

Which of the following is true for the standard enthalpy of formation ($$\Delta H_f^\circ) of an $$element in its most stable form at 298 K?

Accepted Answer

$$\Delta H_f^\circ is $$zero.

Question 14

Which of the following equations correctly relates the change in entropy to the number of microstates ($$W$$)?

Accepted Answer

$$S = k \ln W$$

Question 15

A chemical reaction is carried out in a bomb calorimeter. Which of the following is true?

Accepted Answer

The heat measured is equal to the change in internal energy ($$\Delta U).$$

Question 16

Which of the following best explains why the enthalpy of vaporization is greater than the enthalpy of fusion for most substances?

Accepted Answer

Breaking all intermolecular forces requires more energy than partially disrupting them.

Question 17

Which of the following is the correct relationship for calculating the standard reaction entropy ($$\Delta S^\circ$$)?

Accepted Answer

$$\Delta S^\circ = \sum n S^\circ(	ext{products}) - \sum n S^\circ(	ext{reactants})$$

Question 18

Which of the following is a correct statement of the First Law of Thermodynamics?

Accepted Answer

The total energy of an isolated system is constant.

Thermodynamics: Energy, Heat, Work, and Spontaneity in Chemical Systems

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