Question 1

Using the thermodynamic data provided below, calculate Ka for HCN(aq) at 25$\circ$. $\begin{array}{|l|c|c|}
\hline & \Delta \mathrm{H}^\circ_{\mathrm{f}}(\mathrm{~kJ} / \mathrm{mol}) & \mathrm{S}^{\circ}(\mathrm{J} / \mathrm{K} \cdot \mathrm{~mol}) \
\hline \mathrm{H}^{+}(a q) & 0 & 0 \
\hline \mathrm{CN}^{-}(a q) & 151.0 & 117.99 \
\hline \mathrm{HCN}(a q) & 105.4 & 128.9 \
\hline
\end{array}$

Accepted Answer

A)  2.4 * 10-9 
B)  2.6 * 10-9 
C)  2.8 * 10-9 
D)  3.0 * 10-9 
E)  None of the above 
A)  2.4 * 10-9 
B)  2.6 * 10-9 
C)  2.8 * 10-9 
D)  3.0 * 10-9 
E)  None of the above

Question 2

Sulfur can be separated from lead in the mineral galena, PbS(s), by "roasting" the ore in the presence of oxygen as shown in the following reaction: 2PbS(s) + 3O2(g) $\rarr$ 2PbO(s) + 2SO2(g)
Determine $\Delta$G for the above reaction at 850$\circ$C. $\begin{array}{|l|c|c|}
\hline & \Delta \mathrm{H}_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) & \mathrm{S}^{\circ}(\mathrm{J} / \mathrm{K} \cdot \mathrm{~mol}) \
\hline \mathrm{PbS}(s) & -94.3 & 91.2 \
\hline \mathrm{O}_{2}(g) & 0 & 205.0 \
\hline \mathrm{PbO}(s) & -217.86 & 69.45 \
\hline \mathrm{SO}_{2}(g) & -296.4 & 248.5 \
\hline
\end{array}$

Accepted Answer

A)  -620 kJ/mol 
B)  -640 kJ/mol 
C)  -660 kJ/mol 
D)  -680 kJ/mol 
E)  None of the above 
A)  -620 kJ/mol 
B)  -640 kJ/mol 
C)  -660 kJ/mol 
D)  -680 kJ/mol 
E)  None of the above

Question 3

Hydrogen peroxide (H2O2) decomposes according to the equation H2O2(l) $\rarr$ H2O(l) + 1/2O2(g).Calculate Kp for this reaction at 25$\circ$C. $\Delta$H$\circ$= -98.2 kJ/mol, $\Delta$S$\circ$ = 70.1 J/K·mol)

Accepted Answer

A)  1.3 * 10-21 
B)  20.9 
C)  3.46 * 1017 
D)  7.5 * 1020 
E)  8.6 * 104 
A)  1.3 * 10-21 
B)  20.9 
C)  3.46 * 1017 
D)  7.5 * 1020 
E)  8.6 * 104

Question 4

Using the thermodynamic data provided below, calculate Ksp for ZnS(s) at 25$\circ$. $\begin{array}{|l|l|c|}
\hline & \Delta \mathrm{H}^{\circ}_f(\mathrm{kJ} / \mathrm{mol}) & \mathrm{S}^{\circ}(\mathrm{J} / \mathrm{K} \cdot \mathrm{~mol}) \
\hline \mathrm{Zn}^{2+}(a q) & -152.4 & -106.5 \
\hline \mathrm{~S}^{2-}(a q) & 41.8 & 22 \
\hline \mathrm{ZnS}(s) & -203 & 57.7 \
\hline
\end{array}$

Accepted Answer

A)  2.4 * 10-22 
B)  2.4 * 10-24 
C)  2.4 * 10-26 
D)  2.4 * 10-28 
E)  None of the above 
A)  2.4 * 10-22 
B)  2.4 * 10-24 
C)  2.4 * 10-26 
D)  2.4 * 10-28 
E)  None of the above

Question 5

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

Accepted Answer

A)  CO(g) 
B)  CH4(g) 
C)  NaCl(s) 
D)  H2O(l) 
E)  Fe(s) 
A)  CO(g) 
B)  CH4(g) 
C)  NaCl(s) 
D)  H2O(l) 
E)  Fe(s)

Question 6

Which of the following is consistent with an exothermic reaction that is nonspontaneous at high temperatures

Accepted Answer

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

Question 7

Which one of the following reactions would you expect to have the lowest $\Delta$S$\circ$

Accepted Answer

A)  CH4(g) + 2O2(g) $\rarr$ CO2(g) + 2H2O(g) 
B)  C2H2(g) + 5/2O2(g) $\rarr$ 2CO2(g) + H2O(g) 
C)  C2H4(g) + O2(g) $\rarr$2CO2(g) + 2H2O(g) 
D)  C2H6(g) + 7/2O2(g) $\rarr$ 2CO2(g) + 3H2O(g) 
A)  CH4(g) + 2O2(g) $\rarr$ CO2(g) + 2H2O(g) 
B)  C2H2(g) + 5/2O2(g) $\rarr$ 2CO2(g) + H2O(g) 
C)  C2H4(g) + O2(g) $\rarr$2CO2(g) + 2H2O(g) 
D)  C2H6(g) + 7/2O2(g) $\rarr$ 2CO2(g) + 3H2O(g)

Question 8

For the reaction 3H2(g) + N2(g) $\leftrightharpoons$ 2NH3(g), Kc = 9.0 at 350$\circ$C. Calculate $\Delta$G$\circ$ at 350$\circ$C.

Accepted Answer

A)  25.4 kJ/mol 
B)  27.4 kJ/mol 
C)  29.4 kJ/mol 
D)  31.4 kJ/mol 
E)  None of the above 
A)  25.4 kJ/mol 
B)  27.4 kJ/mol 
C)  29.4 kJ/mol 
D)  31.4 kJ/mol 
E)  None of the above

Question 9

For the reaction 2NO(g) + O2(g) $\rarr$ 2NO2(g) if initially P(NO) = 1.5 atm, P(O2) = 1.4 atm, and P(NO2) = 2.0 atm, calculate $\Delta$G for this reaction at 25$\circ$C. The following data is valid at 25$\circ$C: $\begin{array}{|c|c|}
\hline & \Delta \mathrm{G}_{\mathrm{f}}{ }^{\circ}(\mathrm{kJ} / \mathrm{mol}) \
\hline \mathrm{NO} & 86.7 \
\hline \mathrm{NO}_{2} & 51.8 \
\hline
\end{array}$

Accepted Answer

A)  -69.9 kJ/mol 
B)  -69.2 kJ/mol 
C)  522.1 kJ/mol 
D)  -79.9 kJ/mol 
E)  -35.0 kJ/mol 
A)  -69.9 kJ/mol 
B)  -69.2 kJ/mol 
C)  522.1 kJ/mol 
D)  -79.9 kJ/mol 
E)  -35.0 kJ/mol

Question 10

The normal freezing point of ammonia is -78$\circ$C. Predict the signs of $\Delta$H, $\Delta$S, and $\Delta$G for ammonia when it freezes at -80$\circ$C and 1 atm: NH3(l) $\rarr$ NH3(s). $\begin{array}{llll}
&\Delta \mathrm{H} & \Delta \mathrm{S} & \Delta \mathrm{G}\\hline
\text { A. } & - & - & 0 \
\text { B. } & - & + & - \
\text { C. } & + & - & + \
\text { D. } & + & + & 0 \
\text { E. } & - & - & -
\end{array}$

Accepted Answer

A)  A 
B)  B 
C)  C 
D)  D 
E)  E 
A)  A 
B)  B 
C)  C 
D)  D 
E)  E

Question 11

Consider the reaction CO(g) + 2H2(g) $\leftrightharpoons$ CH3OH(l) at 25$\circ$C.
$\Delta$G$\circ$f (CO) = -137.3 kJ/mol 
$\Delta$G$\circ$f (CH3OH) = -166.3 kJ/mol
$\Delta$H$\circ$f (CO) = -110.5 kJ/mol
$\Delta$H$\circ$f (CH3OH) = -238.7 kJ/mol
S$\circ$(CO) = 197.9 J/K·mol
S$\circ$(CH3OH) = 126.8 J/K·mol
Calculate $\Delta$G$\circ$ at 25$\circ$C.

Accepted Answer

A)  -29.0 kJ/mol 
B)  -31.0 kJ/mol 
C)  -33.0 kJ/mol 
D)  -35.0 kJ/mol 
E)  None of the above 
A)  -29.0 kJ/mol 
B)  -31.0 kJ/mol 
C)  -33.0 kJ/mol 
D)  -35.0 kJ/mol 
E)  None of the above

Question 12

The following reaction is nonspontaneous at 25$\circ$C: Cu2O(s) $\rarr$2Cu(s) + 1/2O2(g), $\Delta$G$\circ$ = 141 kJ/mol
If $\Delta$S$\circ$ = 75.8 J/K·mol, what is the lowest temperature at which the reaction will be spontaneous

Accepted Answer

A)  2160 K 
B)  2260 K 
C)  2360 K 
D)  2460 K 
E)  None of the above 
A)  2160 K 
B)  2260 K 
C)  2360 K 
D)  2460 K 
E)  None of the above

Question 13

The entropy of a perfectly ordered crystalline substance at 0 K is 0 J/mol.

Accepted Answer

A) True 
 B)False

Question 14

Which response includes all the following processes that are accompanied by an increase in entropy
1) 2SO2(g) + O2(g) $\rarr$ SO3(g)
2) H2O(l) $\rarr$H2O(s)
3) Br2(l) $\rarr$Br2(g)
4) H2O2(l) $\rarr$ H2O(l) + 1/2O2(g)

Accepted Answer

A)  1, 2, 3, 4 
B)  1, 2 
C)  2, 3, 4 
D)  3, 4 
E)  1, 4 
A)  1, 2, 3, 4 
B)  1, 2 
C)  2, 3, 4 
D)  3, 4 
E)  1, 4

Question 15

The expansion of an ideal gas into a vacuum is expected to be spontaneous at high temperature only.

Accepted Answer

A) True 
 B)False

Question 16

With respect to the system only, a reaction with $\Delta$H > 0 and $\Delta$S < 0 is predicted to be:

Accepted Answer

A)  Spontaneous at all temperatures 
B)  Spontaneous at high temperatures only 
C)  Spontaneous at low temperatures only 
D)  Nonspontaneous at all temperatures 
A)  Spontaneous at all temperatures 
B)  Spontaneous at high temperatures only 
C)  Spontaneous at low temperatures only 
D)  Nonspontaneous at all temperatures

Question 17

With respect to the system only, a reaction with $\Delta$H  0 is predicted to be:

Accepted Answer

A)  Spontaneous at all temperatures 
B)  Spontaneous at high temperatures only 
C)  Spontaneous at low temperatures only 
D)  Nonspontaneous at all temperatures 
A)  Spontaneous at all temperatures 
B)  Spontaneous at high temperatures only 
C)  Spontaneous at low temperatures only 
D)  Nonspontaneous at all temperatures

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
Calculate $\Delta$G at 800 K and 1 atm pressure (assume $\Delta$S$\circ$ and $\Delta$H$\circ$do not change with temperature).

Accepted Answer

A)  -36.66 kJ/mol 
B)  -46.66 kJ/mol 
C)  -56.66 kJ/mol 
D)  -66.66 kJ/mol 
E)  None of the above 
A)  -36.66 kJ/mol 
B)  -46.66 kJ/mol 
C)  -56.66 kJ/mol 
D)  -66.66 kJ/mol 
E)  None of the above

Question 19

For the reaction HCONH2(g) $\leftrightharpoons$ NH3(g) + CO(g), Kc = 4.84 at 400 K. If $\Delta$H$\circ$ for this reaction is 29 kJ/mol, find Kc at 500 K.

Accepted Answer

A)  5.8 
B)  0.17 
C)  27 
D)  0.88 
E)  10.3 
A)  5.8 
B)  0.17 
C)  27 
D)  0.88 
E)  10.3

Question 20

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
Calculate the value of the equilibrium constant (Kp) at 800 K and 1 atm pressure.

Accepted Answer

A)  1.31 * 103 
B)  1.11 * 103 
C)  1.91 * 102 
D)  1.71 * 102 
E)  None of the above 
A)  1.31 * 103 
B)  1.11 * 103 
C)  1.91 * 102 
D)  1.71 * 102 
E)  None of the above

Exam 17: Entropy Free Energy and Equilibrium

Using the thermodynamic data provided below, calculate Ka for HCN(aq) at 25 ∘\circ∘ . \Delta(/) (/\cdot) (aq) 0 0 (aq) 151.0 117.99 (aq) 105.4 128.9

Hydrogen peroxide (H2O2) decomposes according to the equation H2O2(l) →\rarr→ H2O(l) + 1/2O2(g).Calculate Kp for this reaction at 25 ∘\circ∘ C. Δ\DeltaΔ H ∘\circ∘ = -98.2 kJ/mol, Δ\DeltaΔ S ∘\circ∘ = 70.1 J/K·mol)

Using the thermodynamic data provided below, calculate Ksp for ZnS(s) at 25 ∘\circ∘ . \Delta(/) (/\cdot) (aq) -152.4 -106.5 (aq) 41.8 22 (s) -203 57.7

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

Which of the following is consistent with an exothermic reaction that is nonspontaneous at high temperatures

Which one of the following reactions would you expect to have the lowest Δ\DeltaΔ S ∘\circ∘

For the reaction 3H2(g) + N2(g) ⇋\leftrightharpoons⇋ 2NH3(g), Kc = 9.0 at 350 ∘\circ∘ C. Calculate Δ\DeltaΔ G ∘\circ∘ at 350 ∘\circ∘ C.

For the reaction 2NO(g) + O2(g) →\rarr→ 2NO2(g) if initially P(NO) = 1.5 atm, P(O2) = 1.4 atm, and P(NO2) = 2.0 atm, calculate Δ\DeltaΔ G for this reaction at 25 ∘\circ∘ C. The following data is valid at 25 ∘\circ∘ C: \Delta(/) 86.7 51.8

The normal freezing point of ammonia is -78 ∘\circ∘ C. Predict the signs of Δ\DeltaΔ H, Δ\DeltaΔ S, and Δ\DeltaΔ G for ammonia when it freezes at -80 ∘\circ∘ C and 1 atm: NH3(l) →\rarr→ NH3(s). \Delta \Delta \Delta A. - - 0 B. - + - C. + - + D. + + 0 E. - - -

The following reaction is nonspontaneous at 25 ∘\circ∘ C: Cu2O(s) →\rarr→ 2Cu(s) + 1/2O2(g), Δ\DeltaΔ G ∘\circ∘ = 141 kJ/mol If Δ\DeltaΔ S ∘\circ∘ = 75.8 J/K·mol, what is the lowest temperature at which the reaction will be spontaneous

The entropy of a perfectly ordered crystalline substance at 0 K is 0 J/mol.

Which response includes all the following processes that are accompanied by an increase in entropy 1) 2SO2(g) + O2(g) →\rarr→ SO3(g) 2) H2O(l) →\rarr→ H2O(s) 3) Br2(l) →\rarr→ Br2(g) 4) H2O2(l) →\rarr→ H2O(l) + 1/2O2(g)

The expansion of an ideal gas into a vacuum is expected to be spontaneous at high temperature only.

With respect to the system only, a reaction with Δ\DeltaΔ H > 0 and Δ\DeltaΔ S < 0 is predicted to be:

With respect to the system only, a reaction with Δ\DeltaΔ H < 0 and Δ\DeltaΔ S > 0 is predicted to be:

For the reaction HCONH2(g) ⇋\leftrightharpoons⇋ NH3(g) + CO(g), Kc = 4.84 at 400 K. If Δ\DeltaΔ H ∘\circ∘ for this reaction is 29 kJ/mol, find Kc at 500 K.

Chemistry: The Study of Change

Atoms Molecules and Ions

Mass Relationships in Chemical Reactions

Reactions in Aqueous Solutions

Gases

Thermochemistry

Quantum Theory and the Electronic Structure of Atoms

Periodic Relationships Among the Elements

Chemical Bonding I: Basic Concepts

Chemical Bonding II: Molecular Geometry and Hybridization of Atomic

Intermolecular Forces and Liquids and Solids

Physical Properties of Solutions

Chemical Kinetics

Chemical Equilibrium

Acids and Bases

Acid-Base Equilibria and Solubility Equilibria

Electrochemistry

Nuclear Chemistry

Chemistry in the Atmosphere

Metallurgy and the Chemistry of Metals

Nonmetallic Elements and Their Compounds

Transition Metals Chemistry and Coordination Compounds

Organic Chemistry

Synthetic and Natural Organic Polymers

Filters

Using the thermodynamic data provided below, calculate K_a for HCN(aq) at 25^$\circ$. \Delta(/) (/\cdot) (aq) 0 0 (aq) 151.0 117.99 (aq) 105.4 128.9

Hydrogen peroxide (H₂O₂) decomposes according to the equation H₂O₂(l) $\rarr$ H₂O(l) + ¹/₂O₂(g).Calculate K_p for this reaction at 25^$\circ$C. $\Delta$ H^$\circ$= -98.2 kJ/mol, $\Delta$ S^$\circ$ = 70.1 J/K·mol)

Using the thermodynamic data provided below, calculate K_sp for ZnS(s) at 25^$\circ$. \Delta(/) (/\cdot) (aq) -152.4 -106.5 (aq) 41.8 22 (s) -203 57.7

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

Which one of the following reactions would you expect to have the lowest $\Delta$ S^$\circ$

For the reaction 3H₂(g) + N₂(g) $\leftrightharpoons$ 2NH₃(g), K_c = 9.0 at 350^$\circ$C. Calculate $\Delta$ G^$\circ$ at 350^$\circ$C.

For the reaction 2NO(g) + O₂(g) $\rarr$ 2NO₂(g) if initially P(NO) = 1.5 atm, P(O₂) = 1.4 atm, and P(NO₂) = 2.0 atm, calculate $\Delta$ G for this reaction at 25^$\circ$C. The following data is valid at 25^$\circ$C: \Delta(/) 86.7 51.8

The normal freezing point of ammonia is -78^$\circ$C. Predict the signs of $\Delta$ H, $\Delta$ S, and $\Delta$ G for ammonia when it freezes at -80^$\circ$C and 1 atm: NH₃(l) $\rarr$ NH₃(s). \Delta \Delta \Delta A. - - 0 B. - + - C. + - + D. + + 0 E. - - -

The following reaction is nonspontaneous at 25^$\circ$C: Cu₂O(s) $\rarr$ 2Cu(s) + ¹/₂O₂(g), $\Delta$ G^$\circ$ = 141 kJ/mol If $\Delta$ S^$\circ$ = 75.8 J/K·mol, what is the lowest temperature at which the reaction will be spontaneous

Which response includes all the following processes that are accompanied by an increase in entropy 1) 2SO₂(g) + O₂(g) $\rarr$ SO₃(g) 2) H₂O(l) $\rarr$ H₂O(s) 3) Br₂(l) $\rarr$ Br₂(g) 4) H₂O₂(l) $\rarr$ H₂O(l) + ¹/₂O₂(g)

With respect to the system only, a reaction with $\Delta$ H > 0 and $\Delta$ S < 0 is predicted to be:

With respect to the system only, a reaction with $\Delta$ H < 0 and $\Delta$ S > 0 is predicted to be:

For the reaction HCONH₂(g) $\leftrightharpoons$ NH₃(g) + CO(g), K_c = 4.84 at 400 K. If $\Delta$ H^$\circ$ for this reaction is 29 kJ/mol, find K_c at 500 K.