Q: Given the reaction: $$ \ce{N_2$(g) + 3H_2(g) \rightarrow 2NH_3(g)} $$, calculate $$ \Delta S^\circ_{rxn} at 298 K $$using the following standard molar entropies (in $$ \mathrm{J/(mol \cdot K)} $$): $$ S^\circ(\ce{N_2$}) = 191.5 $$, $$ S^\circ(\ce{H_2$}) = 130.6 $$, $$ S^\circ(\ce{NH_3$}) = 192.5 .$$

$$ \Delta S^\circ_{rxn} = 2 \times 192.5 - [191.5 + 3 \times 130.6] = -198.3\ \mathrm{J/(mol \cdot K)} $$

Question 1

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

Accepted Answer

Energy tends to disperse or spread out rather than concentrate.

Question 2

A chemical reaction is spontaneous at room temperature if:

Accepted Answer

$$ \Delta G \u003c 0 $$

Question 3

Which of the following is a state function?

Accepted Answer

Enthalpy ($$ H )$$

Question 4

Consider the melting of ice at 0°C and 1 atm. Which statement is true regarding entropy?

Accepted Answer

Entropy increases because the molecules become more disordered.

Question 5

Which equation correctly relates the standard free energy change to the equilibrium constant $$ K  at $$temperature $$ T $$?

Accepted Answer

$$ \Delta G^\circ = -RT \ln K $$

Question 6

Which of the following processes is considered reversible?

Accepted Answer

Melting ice at 0°C in equilibrium with liquid water

Question 7

Given the reaction: $$ \ce{N_2$(g) + 3H_2(g) \rightarrow 2NH_3(g)} $$, calculate $$ \Delta S^\circ_{rxn}  at 298 K $$using the following standard molar entropies (in $$ \mathrm{J/(mol \cdot K)} $$): $$ S^\circ(\ce{N_2$}) = 191.5 $$, $$ S^\circ(\ce{H_2$}) = 130.6 $$, $$ S^\circ(\ce{NH_3$}) = 192.5 .$$

Accepted Answer

$$ \Delta S^\circ_{rxn} = 2 	imes 192.5 - [191.5 + 3 	imes 130.6] = -198.3\ \mathrm{J/(mol \cdot K)} $$

Question 8

Which of the following factors increases the entropy of a system?

Accepted Answer

Dissolving a solid salt in water

Question 9

A reaction has $$ \Delta H = -100\ \mathrm{kJ} $$ and $$ \Delta S = -200\ \mathrm{J/K} . At $$what temperature does the reaction change from spontaneous to nonspontaneous?

Accepted Answer

$$ T = 500\ \mathrm{K} $$

Question 10

Which of the following best describes a spontaneous process?

Accepted Answer

A process that occurs without outside intervention.

Question 11

The entropy change for the surroundings ($$ \Delta S_{surr} ) $$during a reaction at constant pressure is given by:

Accepted Answer

$$ \Delta S_{surr} = -\frac{\Delta H_{sys}}{T} $$

Question 12

Which of the following is NOT a factor that affects the standard molar entropy of a substance?

Accepted Answer

Atomic number only

Question 13

For the reaction $$ \ce{C_2H_5OH(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l)} $$, which of the following statements is true regarding entropy?

Accepted Answer

Entropy decreases because the number of gas molecules decreases.

Question 14

Which of the following is the correct expression for the standard entropy change of a reaction?

Accepted Answer

$$ \Delta S^\circ_{rxn} = \sum n S^\circ_{products} - \sum n S^\circ_{reactants} $$

Question 15

Which of the following best describes the meaning of Gibbs free energy ($$ \Delta G $$)?

Accepted Answer

The energy available to do work at constant temperature and pressure.

Question 16

If $$ \Delta G^\circ $$ for a reaction is positive, what does this indicate about the equilibrium constant $$ K $$?

Accepted Answer

$$ K \u003c 1 $$

Question 17

Which of the following is true for an irreversible process?

Accepted Answer

It cannot return to its original state without significant changes to the surroundings.

Question 18

Which of the following correctly expresses the relationship between $$ \Delta G $$, $$ \Delta H $$, and $$ \Delta S  at $$constant temperature?

Accepted Answer

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

Question 19

Which of the following is the correct Boltzmann equation for entropy?

Accepted Answer

$$ S = k \ln W $$

Chapter 19: Free Energy and Thermodynamics – Terms, Definitions, Tables, and Formulas

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