Question 1

For a given substance the entropy always increases in the following order:
S (gas) < S (liq) < S (solid).

Accepted Answer

A) True 
 B)False

Question 2

The free energy of formation of nitric oxide, NO, at 1000 K (roughly the temperature in an automobile engine during ignition) is about 78 kJ/mol. Calculate the equilibrium constant Kp for the reaction N2(g) + O2(g) $\leftrightharpoons$ 2NO(g) at this temperature.

Accepted Answer

A)  Kp = 6.9 * 10-9 
B)  Kp = 7.1 *10-9 
C)  Kp = 7.3 * 10-9 
D)  Kp = 7.5 * 10-9 
E)  None of the above 
A)  Kp = 6.9 * 10-9 
B)  Kp = 7.1 *10-9 
C)  Kp = 7.3 * 10-9 
D)  Kp = 7.5 * 10-9 
E)  None of the above

Question 3

At a given temperature, CO2(g) has a higher entropy per mole than CO2(aq).

Accepted Answer

A) True 
 B)False

Question 4

Melting an ionic solid always results in an increase in entropy.

Accepted Answer

A) True 
 B)False

Question 5

Calculate $\Delta$S$\circ$ at 25$\circ$C for the reduction of PbO(s), 2PbO(s) + C(s) $\rarr$ 2Pb(s) + CO2(g) given these absolute entropies: $\begin{array}{lc}
&\mathrm{S}^{\circ}(\mathrm{J} / \mathrm{K} \cdot \mathrm{~mol})\\hline
\mathrm{PbO}(\mathrm{s}) & 69.45 \
\mathrm{C}(\mathrm{s}) & 5.7 \
\mathrm{Pb}(\mathrm{s}) & 64.89 \
\mathrm{CO}_{2}(\mathrm{g}) & 213.6
\end{array}$

Accepted Answer

A)  +198.8 J/K·mol 
B)  +488.0 J/K·mol 
C)  +353.6 J/K·mol 
D)  -203.3 J/K·mol 
E)  +203.3 J/K·mol 
A)  +198.8 J/K·mol 
B)  +488.0 J/K·mol 
C)  +353.6 J/K·mol 
D)  -203.3 J/K·mol 
E)  +203.3 J/K·mol

Question 6

Kw for the auto-ionization of water, H2O(l) $\rarr$H+(aq) + OH- (aq), is 1.0 * 10-14. What are the signs (+/-) of $\Delta$S$\circ$ and $\Delta$H$\circ$ for the reaction at 25$\circ$C

Accepted Answer

A)  ($\Delta$S$\circ$) = (+) and $\Delta$H$\circ$= (+) 
B)  ($\Delta$S$\circ$) = (+) and $\Delta$H$\circ$ = (-) 
C)  ($\Delta$S$\circ$) = (-) and $\Delta$H$\circ$ = (+) 
D)  ($\Delta$S$\circ$) = (-) and $\Delta$H$\circ$ = (-) 
A)  ($\Delta$S$\circ$) = (+) and $\Delta$H$\circ$= (+) 
B)  ($\Delta$S$\circ$) = (+) and $\Delta$H$\circ$ = (-) 
C)  ($\Delta$S$\circ$) = (-) and $\Delta$H$\circ$ = (+) 
D)  ($\Delta$S$\circ$) = (-) and $\Delta$H$\circ$ = (-)

Question 7

The entropy change $\Delta$S$\circ$ for the reaction NH4Cl(s) $\rarr$ NH3(g) + HCl(g) will be negative.

Accepted Answer

A) True 
 B)False

Question 8

The normal melting point of sulfur is 113 $\circ$C. If a sample of solid sulfur is at 95 $\circ$C, predict the signs of $\Delta$H, $\Delta$S, and $\Delta$G for the melting process at this temperature.

Accepted Answer

A)  ($\Delta$H) > 0, $\Delta$S > 0, $\Delta$G  0, $\Delta$S > 0, $\Delta$G > 0 
C)  ($\Delta$H) > 0, $\Delta$S  0, $\Delta$G > 0 
E)  ($\Delta$H)  0 
A)  ($\Delta$H) > 0, $\Delta$S > 0, $\Delta$G  0, $\Delta$S > 0, $\Delta$G > 0 
C)  ($\Delta$H) > 0, $\Delta$S  0, $\Delta$G > 0 
E)  ($\Delta$H)  0

Question 9

Nitrosyl chloride (NOCl) decomposes at elevated temperatures according to the equation 2NOCl(g) $\leftrightharpoons$ 2NO(g) + Cl2(g). Calculate Kp for this reaction at 227$\circ$C. ($\Delta$H$\circ$ = 81.2 kJ/mol, $\Delta$S$\circ$ = 128 J/K·mol)

Accepted Answer

A)  1.59 * 10-2 
B)  2.10 * 10-7 
C)  62.8 
D)  4.90 * 106 
E)  3.20 * 109 
A)  1.59 * 10-2 
B)  2.10 * 10-7 
C)  62.8 
D)  4.90 * 106 
E)  3.20 * 109

Question 10

Which of the following processes would be accompanied by an increase in entropy

Accepted Answer

A) H2O(g) $\rarr$ H2O(s) 
B) H2O(l) $\rarr$ H2O(s) 
C) H2O(g) $\rarr$ H2O(l) 
D) H2O(s) $\rarr$ H2O(g) 
E)  H2O(l, 50$\circ$
C)  $\rarr$ H2O(l, 25$\circ$
C)  
A) H2O(g) $\rarr$ H2O(s) 
B) H2O(l) $\rarr$ H2O(s) 
C) H2O(g) $\rarr$ H2O(l) 
D) H2O(s) $\rarr$ H2O(g) 
E)  H2O(l, 50$\circ$
C)  $\rarr$ H2O(l, 25$\circ$
C)

Question 11

Calculate $\Delta$G$\circ$ for the combustion of ethanol vapor, C2H5OH(g), at 750$\circ$C in oxygen to form carbon dioxide and water vapor. The following data is valid at 25$\circ$C: $\begin{array}{lcc}
&\Delta \mathrm{H}_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) & \Delta \mathrm{G}_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol})\\hline
\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{~g}) & -234.8 & -167.9 \
\mathrm{O}_{2}(\mathrm{g}) & 0 & 0 \
\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) & -241.8 & -228.6 \
\mathrm{CO}_{2}(\mathrm{g}) & -393.5 & -394.4
\end{array}$

Accepted Answer

A)  -1407 kJ/mol 
B)  -2151 kJ/mol 
C)  -1307 kJ/mol 
D)  -4486 kJ/mol 
E)  -1377 kJ/mol 
A)  -1407 kJ/mol 
B)  -2151 kJ/mol 
C)  -1307 kJ/mol 
D)  -4486 kJ/mol 
E)  -1377 kJ/mol

Question 12

For a certain reaction, $\Delta$G$\circ$ = 87 kJ/mol, $\Delta$H$\circ$ = 100 kJ/mol at STP. At what temperature, in K, is the reaction at equilibrium, assuming that $\Delta$S$\circ$and $\Delta$H$\circ$ are temperature-independent

Accepted Answer

A)  1,700 K 
B)  1,900 K 
C)  2,100 K 
D)  2,300 K 
E)  None of the above 
A)  1,700 K 
B)  1,900 K 
C)  2,100 K 
D)  2,300 K 
E)  None of the above

Question 13

Which of these species has the highest entropy (S$\circ$) at 25$\circ$C

Accepted Answer

A)  CH3OH(l) 
B)  CO(g) 
C)  MgCO3(s) 
D)  H2O(l) 
E)  Ni(s) 
A)  CH3OH(l) 
B)  CO(g) 
C)  MgCO3(s) 
D)  H2O(l) 
E)  Ni(s)

Question 14

For the reaction CuS(s) + H2(g) $\leftrightharpoons$ H2S(g) + Cu(s), 
$\Delta$G$\circ$f (CuS) = -53.6 kJ/mol
$\Delta$G$\circ$f (H2S) = -33.6 kJ/mol
$\Delta$H$\circ$f (CuS) = -53.1 kJ/mol
$\Delta$H$\circ$f (H2S) = - 20.6 kJ/mol
Calculate the value of the equilibrium constant (Kp) for this reaction at 298 K.

Accepted Answer

A)  2.71 * 10-4 
B)  2.91 * 10-4 
C)  3.11 * 10-4 
D)  3.31 * 10-4 
E)  None of the above 
A)  2.71 * 10-4 
B)  2.91 * 10-4 
C)  3.11 * 10-4 
D)  3.31 * 10-4 
E)  None of the above

Question 15

Which of the following is consistent with a spontaneous process in the forward direction

Accepted Answer

A) ($\Delta$Suniv) > 0, $\Delta$G univ > 0 
B) ($\Delta$Suniv)  0, T$\Delta$Suniv univ) > 0, $\Delta$G univ univ) univ univ) > 0, $\Delta$G > 0, T$\Delta$Suniv > 0 
A) ($\Delta$Suniv) > 0, $\Delta$G univ > 0 
B) ($\Delta$Suniv)  0, T$\Delta$Suniv univ) > 0, $\Delta$G univ univ) univ univ) > 0, $\Delta$G > 0, T$\Delta$Suniv > 0

Question 16

The standard free energy of formation of gaseous hydrogen iodide is 1.30 kJ/mol at 25$\circ$C. Find Kp for the reaction H2(g) + I2(s) $\leftrightharpoons$ 2HI(g) at this temperature.

Accepted Answer

A)  7.0 
B)  7100 
C)  1.0 
D)  2.4 
E)  2.9 
A)  7.0 
B)  7100 
C)  1.0 
D)  2.4 
E)  2.9

Question 17

Calculate the free energy of formation of NaBr(s) given the following information: NaBr(s) $\rarr$Na(s) + 1/2Br2(l), $\Delta$G$\circ$ = 349 kJ/mol

Accepted Answer

A)  -309 kJ/mol 
B)  -329 kJ/mol 
C)  -349 kJ/mol 
D)  -369 kJ/mol 
E)  None of the above 
A)  -309 kJ/mol 
B)  -329 kJ/mol 
C)  -349 kJ/mol 
D)  -369 kJ/mol 
E)  None of the above

Question 18

For the reaction SbCl5(g) $\leftrightharpoons$ SbCl3(g) + Cl2(g),
$\Delta$G$\circ$f (SbCl5) = -334.34 kJ/mol
$\Delta$G$\circ$f (SbCl3) = -301.25 kJ/mol
$\Delta$H$\circ$f (SbCl5) = -394.34 kJ/mol
$\Delta$H$\circ$f (SbCl3) = -313.80 kJ/mol
This reaction proceeds spontaneously at 298 K and 1 atm pressure.

Accepted Answer

A) True 
 B)False

Question 19

Predict the normal boiling point of triethylborane (C6H15B) using the following data: $\begin{array}{lcc}
&\Delta \mathrm{H}^{\circ}{ }_{\mathrm{f}}\left(25^{\circ} \mathrm{C}\right) & \Delta \mathrm{G}^{\circ}_\mathrm{f}\left(25^{\circ} \mathrm{C}\right)\\hline
\mathrm{C}_{6} \mathrm{H}_{15} \mathrm{~B}(\mathrm{l}) & -194.6 \mathrm{~kJ} / \mathrm{mol} & 9.4 \mathrm{~kJ} / \mathrm{mol} \
\mathrm{C}_{6} \mathrm{H}_{15} \mathrm{~B}(\mathrm{g}) & -157.7 \mathrm{~kJ} / \mathrm{mol} & 16.1 \mathrm{~kJ} / \mathrm{mol}
\end{array}$

Accepted Answer

A)  92$\circ$C 
B)  -21$\circ$C 
C)  21$\circ$C 
D)  365$\circ$C 
E)  256$\circ$C 
A)  92$\circ$C 
B)  -21$\circ$C 
C)  21$\circ$C 
D)  365$\circ$C 
E)  256$\circ$C

Question 20

Calculate the equilibrium constant for the decomposition of water 2H2O(l) $\leftrightharpoons$ 2H2(g) + O2(g)
At 25$\circ$C, given that $\Delta$G$\circ$f (H2O(l)) = -237.2 kJ/mol.

Accepted Answer

A)  0.83 
B)  6.3 * 10-84 
C)  2.5 * 10-42 
D)  1.6 * 1083 
E)  4.7 * 105 
A)  0.83 
B)  6.3 * 10-84 
C)  2.5 * 10-42 
D)  1.6 * 1083 
E)  4.7 * 105

Exam 17: Entropy Free Energy and Equilibrium

For a given substance the entropy always increases in the following order: S (gas) < S (liq) < S (solid).

The free energy of formation of nitric oxide, NO, at 1000 K (roughly the temperature in an automobile engine during ignition) is about 78 kJ/mol. Calculate the equilibrium constant Kp for the reaction N2(g) + O2(g) ⇋\leftrightharpoons⇋ 2NO(g) at this temperature.

At a given temperature, CO2(g) has a higher entropy per mole than CO2(aq).

Melting an ionic solid always results in an increase in entropy.

Calculate Δ\DeltaΔ S ∘\circ∘ at 25 ∘\circ∘ C for the reduction of PbO(s), 2PbO(s) + C(s) →\rarr→ 2Pb(s) + CO2(g) given these absolute entropies: (/\cdot) () 69.45 () 5.7 () 64.89 () 213.6

Kw for the auto-ionization of water, H2O(l) →\rarr→ H+(aq) + OH- (aq), is 1.0 * 10-14. What are the signs (+/-) of Δ\DeltaΔ S ∘\circ∘ and Δ\DeltaΔ H ∘\circ∘ for the reaction at 25 ∘\circ∘ C

The entropy change Δ\DeltaΔ S ∘\circ∘ for the reaction NH4Cl(s) →\rarr→ NH3(g) + HCl(g) will be negative.

The normal melting point of sulfur is 113 ∘\circ∘ C. If a sample of solid sulfur is at 95 ∘\circ∘ C, predict the signs of Δ\DeltaΔ H, Δ\DeltaΔ S, and Δ\DeltaΔ G for the melting process at this temperature.

Nitrosyl chloride (NOCl) decomposes at elevated temperatures according to the equation 2NOCl(g) ⇋\leftrightharpoons⇋ 2NO(g) + Cl2(g). Calculate Kp for this reaction at 227 ∘\circ∘ C. ( Δ\DeltaΔ H ∘\circ∘ = 81.2 kJ/mol, Δ\DeltaΔ S ∘\circ∘ = 128 J/K·mol)

Which of the following processes would be accompanied by an increase in entropy

Calculate Δ\DeltaΔ G ∘\circ∘ for the combustion of ethanol vapor, C2H5OH(g), at 750 ∘\circ∘ C in oxygen to form carbon dioxide and water vapor. The following data is valid at 25 ∘\circ∘ C: \Delta(/) \Delta(/) () -234.8 -167.9 () 0 0 () -241.8 -228.6 () -393.5 -394.4

For a certain reaction, Δ\DeltaΔ G ∘\circ∘ = 87 kJ/mol, Δ\DeltaΔ H ∘\circ∘ = 100 kJ/mol at STP. At what temperature, in K, is the reaction at equilibrium, assuming that Δ\DeltaΔ S ∘\circ∘ and Δ\DeltaΔ H ∘\circ∘ are temperature-independent

Which of these species has the highest entropy (S ∘\circ∘ ) at 25 ∘\circ∘ C

Which of the following is consistent with a spontaneous process in the forward direction

The standard free energy of formation of gaseous hydrogen iodide is 1.30 kJ/mol at 25 ∘\circ∘ C. Find Kp for the reaction H2(g) + I2(s) ⇋\leftrightharpoons⇋ 2HI(g) at this temperature.

Calculate the free energy of formation of NaBr(s) given the following information: NaBr(s) →\rarr→ Na(s) + 1/2Br2(l), Δ\DeltaΔ G ∘\circ∘ = 349 kJ/mol

Predict the normal boiling point of triethylborane (C6H15B) using the following data: \Delta 2 \Delta 2 () -194.6/ 9.4/ () -157.7/ 16.1/

Calculate the equilibrium constant for the decomposition of water 2H2O(l) ⇋\leftrightharpoons⇋ 2H2(g) + O2(g) At 25 ∘\circ∘ C, given that Δ\DeltaΔ G ∘\circ∘ f (H2O(l)) = -237.2 kJ/mol.

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The free energy of formation of nitric oxide, NO, at 1000 K (roughly the temperature in an automobile engine during ignition) is about 78 kJ/mol. Calculate the equilibrium constant K_p for the reaction N₂(g) + O₂(g) $\leftrightharpoons$ 2NO(g) at this temperature.

At a given temperature, CO₂(g) has a higher entropy per mole than CO₂(aq).

Calculate $\Delta$ S^$\circ$ at 25^$\circ$C for the reduction of PbO(s), 2PbO(s) + C(s) $\rarr$ 2Pb(s) + CO₂(g) given these absolute entropies: (/\cdot) () 69.45 () 5.7 () 64.89 () 213.6

K_w for the auto-ionization of water, H₂O(l) $\rarr$ H⁺(aq) + OH^- (aq), is 1.0 * 10^-14. What are the signs (+/-) of $\Delta$ S^$\circ$ and $\Delta$ H^$\circ$ for the reaction at 25^$\circ$C

The entropy change $\Delta$ S^$\circ$ for the reaction NH₄Cl(s) $\rarr$ NH₃(g) + HCl(g) will be negative.

The normal melting point of sulfur is 113 ^$\circ$C. If a sample of solid sulfur is at 95 ^$\circ$C, predict the signs of $\Delta$ H, $\Delta$ S, and $\Delta$ G for the melting process at this temperature.

Nitrosyl chloride (NOCl) decomposes at elevated temperatures according to the equation 2NOCl(g) $\leftrightharpoons$ 2NO(g) + Cl₂(g). Calculate K_p for this reaction at 227^$\circ$C. ( $\Delta$ H^$\circ$ = 81.2 kJ/mol, $\Delta$ S^$\circ$ = 128 J/K·mol)

Calculate $\Delta$ G^$\circ$ for the combustion of ethanol vapor, C₂H₅OH(g), at 750^$\circ$C in oxygen to form carbon dioxide and water vapor. The following data is valid at 25^$\circ$C: \Delta(/) \Delta(/) () -234.8 -167.9 () 0 0 () -241.8 -228.6 () -393.5 -394.4

For a certain reaction, $\Delta$ G^$\circ$ = 87 kJ/mol, $\Delta$ H^$\circ$ = 100 kJ/mol at STP. At what temperature, in K, is the reaction at equilibrium, assuming that $\Delta$ S^$\circ$and $\Delta$ H^$\circ$ are temperature-independent

Which of these species has the highest entropy (S^$\circ$) at 25^$\circ$C

The standard free energy of formation of gaseous hydrogen iodide is 1.30 kJ/mol at 25^$\circ$C. Find K_p for the reaction H₂(g) + I₂(s) $\leftrightharpoons$ 2HI(g) at this temperature.

Calculate the free energy of formation of NaBr(s) given the following information: NaBr(s) $\rarr$ Na(s) + ¹/₂Br₂(l), $\Delta$ G^$\circ$ = 349 kJ/mol

Predict the normal boiling point of triethylborane (C₆H₁₅B) using the following data: \Delta 2 \Delta 2 () -194.6/ 9.4/ () -157.7/ 16.1/

Calculate the equilibrium constant for the decomposition of water 2H₂O(l) $\leftrightharpoons$ 2H₂(g) + O₂(g) At 25^$\circ$C, given that $\Delta$ G^$\circ$_f (H₂O(l)) = -237.2 kJ/mol.