Q: Which of the following equations is used to calculate the standard enthalpy change of a reaction?

$$\Delta H^\circ = \Sigma n \Delta_f H^\circ (\text{products}) - \Sigma m \Delta_f H^\circ (\text{reactants})$$

Question 1

Which of the following best describes an extensive property, and which is an example of it?

Accepted Answer

It depends on the amount of substance; mass is an example.

Question 2

A chemical reaction occurs in a closed system at constant pressure. Which thermodynamic quantity is most useful for determining the heat exchanged with the surroundings?

Accepted Answer

Enthalpy ($$H)$$

Question 3

Which of the following statements about state functions is correct?

Accepted Answer

State functions depend only on the initial and final states, not on the path taken.

Question 4

A reaction has $$\Delta H = -100 kJ $$and $$\Delta S = +200 J/K. At$$ $$T = 298 K$$, what is the sign of $$\Delta G$$ and is the reaction spontaneous?

Accepted Answer

$$\Delta G is $$negative; the reaction is spontaneous.

Question 5

Which of the following best describes the Second Law of Thermodynamics?

Accepted Answer

The entropy of the universe increases for spontaneous processes.

Question 6

Given the reaction: $$2SO_2(g) + O_2$(g) \rightarrow 2SO_3(g)$$, with $$\Delta_f H^\circ(SO_3$) = -395.2 kJ/$$mol, $$\Delta_f H^\circ(SO_2$) = -296.1 kJ/$$mol, and $$\Delta_f H^\circ(O_2$) = 0 kJ/$$mol, calculate $$\Delta_r H^\circ$$ for the reaction.

Accepted Answer

$$-198.2 kJ$$

Question 7

Which of the following scenarios describes an isolated system?

Accepted Answer

A thermos bottle that prevents both heat and matter exchange with the environment.

Question 8

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

Accepted Answer

$$\Delta U = Q + W$$

Question 9

A 50.0 g sample of water is heated from 20.0°C to 30.0°C. Given $$c_{water} = 4.18 J/g$$·K, how much heat ($$q) is $$absorbed?

Accepted Answer

$$q = 2,090 J$$

Question 10

Which of the following processes is always exothermic?

Accepted Answer

Combustion of octane in air.

Question 11

Which of the following is an example of an intensive property?

Accepted Answer

Density

Question 12

Which of the following best describes the Third Law of Thermodynamics?

Accepted Answer

The entropy of a perfect crystal at absolute zero is zero.

Question 13

Which of the following reactions is most likely to have a positive entropy change ($$\Delta S \u003e 0$$)?

Accepted Answer

$$CaCO_3(s$$) \rightarrow CaO(s) + $$CO_2(g$$)$$

Question 14

A reaction has $$\Delta H = +50 kJ $$and $$\Delta S = +200 J/K. At $$what temperature will the reaction become spontaneous?

Accepted Answer

At temperatures above $$250 K$$

Question 15

Which of the following is true for a spontaneous process at constant temperature and pressure?

Accepted Answer

$$\Delta G \u003c 0$$

Question 16

Which of the following is NOT a state function?

Accepted Answer

Work ($$W)$$

Question 17

Which of the following best explains why water has a high specific heat capacity?

Accepted Answer

It requires more energy to raise the temperature of water compared to most other substances.

Question 18

Which of the following equations is used to calculate the standard enthalpy change of a reaction?

Accepted Answer

$$\Delta H^\circ = \Sigma n \Delta_f H^\circ (	ext{products}) - \Sigma m \Delta_f H^\circ (	ext{reactants})$$

Question 19

Which of the following is true about the standard enthalpy of formation ($$\Delta_f H^\circ) $$for an element in its most stable form?

Accepted Answer

It is zero.

Question 20

Which of the following best describes the relationship between enthalpy ($$H$$), internal energy ($$U$$), pressure ($$P$$), and volume ($$V$$)?

Accepted Answer

$$H = U + PV$$

Chemical Thermodynamics: Energy, Enthalpy, Entropy, and Gibbs Free Energy

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