Question 1

Which of the following statements best describes an exothermic process?

Accepted Answer

The system releases heat to the surroundings, resulting in a negative $$q.$$

Question 2

A 50.0 g sample of metal at $$100\ ^\circ\mathrm{C} is $$placed in 100.0 g of water at $$25.0\ ^\circ\mathrm{C}. $$The final temperature is $$30.0\ ^\circ\mathrm{C}. If $$the specific heat of water is $$4.184\ \mathrm{J/g\cdot K}$$, what is the specific heat capacity ($$c_s) of $$the metal? (Assume no heat loss to surroundings.)

Accepted Answer

$$0.385\ \mathrm{J/g\cdot K}$$

Question 3

Which of the following phase changes is typically endothermic?

Accepted Answer

Sublimation

Question 4

Given the reaction: $$\mathrm{C(graphite) + 2H_2(g) \rightarrow CH_4$(g)}$$, and the following enthalpies of formation: $$\Delta H_f^\circ(\mathrm{CH_4$(g)}) = -74.8\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{H_2$(g)}) = 0$$, $$\Delta H_f^\circ(\mathrm{C(graphite)}) = 0$$, what is $$\Delta H_{rxn}$$?

Accepted Answer

$$-74.8\ \mathrm{kJ}$$

Question 5

Which of the following best explains why the entropy ($$S) $$increases when a solid sublimes to a gas?

Accepted Answer

The degrees of freedom and randomness of the particles increase.

Question 6

A chemical reaction has $$\Delta H = +40\ \mathrm{kJ}$$ and $$\Delta S = +120\ \mathrm{J/K}. At $$what minimum temperature (in K) will this reaction become spontaneous?

Accepted Answer

$$333\ \mathrm{K}$$

Question 7

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

Accepted Answer

$$\Delta G \u003c 0$$

Question 8

Which of the following statements about bond dissociation enthalpy is correct?

Accepted Answer

Bond dissociation enthalpy is always endothermic because energy is required to break a bond.

Question 9

Consider the reaction: $$\mathrm{N_2$(g) + 3H_2(g) \rightarrow 2NH_3(g)}. If $$the entropy change $$\Delta S_{rxn} is $$negative, which of the following best explains why?

Accepted Answer

The reaction consumes more moles of gas than it produces.

Question 10

A solution of ammonium nitrate in water feels cold to the touch. Which of the following best describes the thermodynamic process?

Accepted Answer

The dissolution is endothermic and may be spontaneous if $$\Delta S is $$sufficiently positive.

Question 11

Which of the following is a state function?

Accepted Answer

Enthalpy ($$H)$$

Question 12

If $$\Delta G^\circ_{rxn} \u003c 0$$ for a reaction at standard conditions, which of the following is true about the equilibrium constant $$K$$?

Accepted Answer

$$K \u003e 1$$

Question 13

Which of the following best describes the sign of $$\Delta S_{surr}$$ for an exothermic reaction at constant temperature?

Accepted Answer

$$\Delta S_{surr} is $$positive because heat is released to the surroundings.

Question 14

Which of the following is NOT a correct statement about entropy?

Accepted Answer

Entropy is always positive for all processes.

Question 15

A reaction has $$\Delta H = -50\ \mathrm{kJ}$$ and $$\Delta S = -100\ \mathrm{J/K}. At $$what temperature (in K) does the reaction change from spontaneous to nonspontaneous?

Accepted Answer

$$500\ \mathrm{K}$$

Question 16

Which of the following best explains why the entropy of $$\mathrm{H_2O(l)} is $$less than that of $$\mathrm{H_2O(g)} at $$the same temperature?

Accepted Answer

Liquid water has fewer degrees of freedom due to intermolecular forces.

Question 17

Which of the following is true about the spontaneity of a process?

Accepted Answer

A process is spontaneous if $$\Delta S_{univ} \u003e 0.$$

Question 18

Which of the following best describes the effect of temperature on the spontaneity of an endothermic process with a positive entropy change?

Accepted Answer

Increasing temperature makes the process more likely to be spontaneous.

Question 19

Which of the following is the correct expression for the entropy change of the surroundings at constant temperature?

Accepted Answer

$$\Delta S_{surr} = -\dfrac{q_{sys}}{T}$$

Question 20

Which of the following statements about the equilibrium constant $$K$$ and Gibbs free energy is correct?

Accepted Answer

If $$K \u003e 1$$, $$\Delta G^\circ_{rxn} is $$negative and the reaction is product-favored.

Thermochemistry and Spontaneity: Energy, Enthalpy, Entropy, and Free Energy

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