Deck 16: Spontaneity of Reaction

Question 1

The dissolution of ammonium nitrate occurs spontaneously in water at 25°C.As NH₄NO₃ dissolves,the temperature of the water decreases.What are the signs of ΔH,ΔS,and ΔG for this process?

A) ΔH > 0,ΔS < 0,ΔG > 0
B) ΔH > 0,ΔS > 0,ΔG > 0
C) ΔH > 0,ΔS > 0,ΔG < 0
D) ΔH < 0,ΔS < 0,ΔG < 0
E) ΔH < 0,ΔS > 0,ΔG > 0

Answer 1

ΔH > 0,ΔS > 0,ΔG < 0

Question 2

Calculate ΔS° for the following reaction, H₂(g)+ Br₂(l)→ 2HBr(g)
Given S°[H₂(g)] = +131 J/mol⋅K,S°[Br₂(l)] = +152 J/mol⋅K,and S°[HBr(g)] = +199 J/mol⋅K.

A) −84 J/K
B) +84 J/K
C) +115 J/K
D) +482 J/K
E) +681 J/K

Answer 2

−84 J/K

Question 3

If a chemical reaction has a negative change in entropy,ΔS,then

A) the reaction is endothermic.
B) the reaction is spontaneous.
C) the equilibrium constant is greater than 1.
D) there is an increase in the order of the system.
E) the change in Gibbs free energy,ΔG,is negative.

Answer 3

there is an increase in the order of the system.

Question 4

All of the following statements are true EXCEPT

A) a reaction is spontaneous if ΔG < 0.
B) if ΔG = 0,the system is at equilibrium.
C) if ΔG = 0,then ΔS = ΔH.
D) if ΔG > 0,then a reaction is not spontaneous.
E) ΔG is referred to as Gibbs free energy.

Question 5

All of the following events result in an increase in entropy EXCEPT

A) the melting of candle wax.
B) the combustion of carbon.
C) the dissolution of sodium chloride in water.
D) the evaporation of ethanol.
E) the formation of N₂O₄(g)from NO₂(g).

Question 6

For which of the following reactions will the entropy of the system decrease?

A) 2NH₃(g)→ N₂(g)+ 3H₂(g)
B) 2C(s)+ O₂(g)→ 2CO(g)
C) CaCO₃(s)→ CaO(s)+ CO₂(g)
D) 2NO₂(g)→ N₂O₄(g)
E) NaOH(s)→ Na⁺(aq)+ OH^-(aq)

Question 7

If ΔG is positive at all temperatures,then which of the following statements must be true?

A) ΔH < 0 and ΔS < 0
B) ΔH < 0 and ΔS = 0
C) ΔH < 0 and ΔS > 0
D) ΔH > 0 and ΔS > 0
E) ΔH > 0 and ΔS < 0

Question 8

When a real gas is compressed from low pressure to a higher pressure,its temperature increases.Predict the signs of ΔH and ΔS.

A) ΔH < 0 and ΔS < 0
B) ΔH < 0 and ΔS > 0
C) ΔH > 0 and ΔS < 0
D) ΔH > 0 and ΔS > 0
E) ΔH < 0 and ΔS = 0

Question 9

All of the following statements are true EXCEPT

A) ΔS > 0 for systems that become more disorderly.
B) reactions are spontaneous when ΔG < 0.
C) reactions are spontaneous when ΔH < 0.
D) ΔH < 0 for exothermic reactions.
E) generally,nature tends to move from more ordered to more random states.

Question 10

All of the following statements are true EXCEPT

A) for a given material,the gas has greater entropy than the solid.
B) the entropy for gaseous elements is zero at 298 K.
C) at 0 K,an ordered pure crystalline solid has an entropy of zero.
D) for a given material,the liquid has greater entropy than the solid.
E) increasing the temperature of a substance increases its entropy.

Question 11

Which of the following linear chain alcohols is likely to have the largest standard molar entropy in the liquid state?

A) CH₃OH
B) CH₃CH₂OH
C) CH₃CH₂CH₂OH
D) CH₃CH₂CH₂CH₂OH
E) CH₃CH₂CH₂CH₂CH₂OH

Question 12

If a chemical reaction is exothermic,but not spontaneous,which of the following must be true?

A) ΔG > 0,ΔS > 0 and ΔH > 0
B) ΔG < 0,ΔS > 0 and ΔH > 0
C) ΔG > 0,ΔS < 0 and ΔH > 0
D) ΔG < 0,ΔS < 0 and ΔH < 0
E) ΔG > 0,ΔS < 0 and ΔH < 0

Question 13

Calculate ΔS° for the following reaction, 2SO₂(g)+ O₂(g)→ 2SO₃(g)
Given S°[SO₂(g)] = 248.2 J/mol⋅K,S°[O₂(g)] = 205.1 J/mol⋅K,and S°[SO₃(g)] = 256.8 J/mol⋅K.

A) -196.5 J/K
B) -94.0 J/K
C) -187.9 J/K
D) +187.9 J/K
E) +196.5 J/K

Question 14

Calculate ΔS° for the evaporation of water,given S°[H₂O(l)] = +69.9 J/mol⋅K and S°[H₂O(g)] = +188.7 J/mol⋅K.

A) −258.6 J/K
B) −118.8 J/K
C) 0.0000 J/K
D) +118.8 J/K
E) +258.6 J/K

Question 15

Which of the following reactions is likely to have the most positive change in entropy?

A) N₂(g)+ 3H₂(g)→ 2NH₃(g)
B) N₂(g)+ 2O₂(g)→ 2NO₂(g)
C) 2C(s)+ O₂(g)→ 2CO(g)
D) C(s)+ O₂(g)→ CO₂(g)
E) CaO(s)+ CO₂(g)→ CaCO₃(s)

Question 16

Predict the signs of ΔS and ΔH for the evaporation of water at 295 K.

A) ΔH = 0 and ΔS > 0
B) ΔH > 0 and ΔS < 0
C) ΔH > 0 and ΔS > 0
D) ΔH < 0 and ΔS > 0
E) ΔH < 0 and ΔS < 0

Question 17

All of the following statements are false for the freezing of water at 273 K EXCEPT

A) ΔH < 0.
B) ΔH > 0.
C) ΔH = 0.
D) ΔS = 0.
E) ΔS > 0.

Question 18

Predict the sign of ΔS and ΔH for the combustion of gasoline at 500 K.

A) ΔH > 0 and ΔS > 0
B) ΔH > 0 and ΔS = 0
C) ΔH < 0 and ΔS > 0
D) ΔH < 0 and ΔS < 0
E) ΔH < 0 and ΔS = 0

Question 19

The second law of thermodynamics states that

A) in a spontaneous process,there is a net increase in entropy,taking into account both the system and the surroundings.
B) there is no disorder in a perfect crystal at 0 K.
C) the total energy of the universe is always increasing.
D) the total energy of the universe is constant.
E) mass and energy are conserved in all chemical reactions.

Question 20

Diluting concentrated sulfuric acid with water can be dangerous.The temperature of the solution can increase rapidly.What are the signs of ΔH,ΔS,and ΔG for this process?

A) ΔH < 0,ΔS > 0,ΔG < 0
B) ΔH < 0,ΔS < 0,ΔG < 0
C) ΔH < 0,ΔS > 0,ΔG > 0
D) ΔH > 0,ΔS > 0,ΔG < 0
E) ΔH > 0,ΔS < 0,ΔG > 0

Question 21

Calculate ?G° for the following reaction at 298 K. S(s)+ O₂(g)? SO₂(g)
$\begin{array}{l}\begin{array}{lll}\text { Substance } & \Delta H_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) &S^{\circ}(\mathrm{kJ} / \mathrm{mol} . \mathrm{K})\\\hline \mathrm{S}(s) & 0.0 & +0.0318 \\\mathrm{O}_{2}(g) & 0.0 & +0.2050 \\\mathrm{SO}_{2}(g) & -296.8 & +0.2481\end{array}\end{array}$

A) ?300.2 kJ
B) ?296.8 kJ
C) ?85.1 kJ
D) +29.3 kJ
E) +145.7 kJ

Question 22

For the dimerization of nitrogen dioxide,ΔG° = −4.7 kJ at 25°C. 2NO₂(g)→ N₂O₄(g)
Calculate ΔG for this reaction if the partial pressures of NO₂ and N₂O₄ are both 0.50 atm.(R = 8.31 × 10−³ kJ/K)

A) −6.4 kJ
B) −4.8 kJ
C) −4.7 kJ
D) −4.6 kJ
E) −3.0 kJ

Question 23

Calculate ?S° for the dissociation of dinitrogen tetraoxide at 25°C. N₂O₄(g)? 2NO₂(g)
$\begin{array}{lll}\text { Substance } & \Delta G_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) & \Delta H_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) \\\hline \mathrm{NO}_{2}(g) & +51.3 & +33.2 \\\mathrm{~N}_{2} \mathrm{O}_{4}(g) & +97.9 & +9.2\end{array}$

A) ?2.10 kJ/K
B) ?0.550 kJ/K
C) ?0.208 kJ/K
D) +0.076 kJ/K
E) +2.10 kJ/K

Question 24

The standard free energy change associated with the dissolution of ammonium nitrate in water is -6.73 kJ at 298 K. NH₄NO₃(s) ? NH₄NO₃(aq)
What is the equilibrium constant for the reaction? (R = 8.31 × 10?³ kJ/K)

A) 1.9 × 10^-3
B) 6.6 × 10^-2
C) 1.0
D) 15
E) 5.2 × 10²

Question 25

If ΔG is negative at all temperatures,then which of the following statements must be true?

A) ΔH < 0 and ΔS < 0
B) ΔH < 0 and ΔS = 0
C) ΔH < 0 and ΔS > 0
D) ΔH > 0 and ΔS > 0
E) ΔH > 0 and ΔS < 0

Question 26

Ammonia is synthesized from nitrogen and hydrogen gases. N₂(g)+ 3H₂(g)→ 2NH₃(g)
If ΔH° = −92.2 kJ and ΔS° = −0.1987 kJ/K,at what temperature will ΔG° = 0?

A) 0.00216 K
B) 18.3 K
C) 92.0 K
D) 464 K
E) 672 K

Question 27

Calculate ΔG° for the reaction below at 25.0°C CS₂(g)+ 3Cl₂(g)→ S₂Cl₂(g)+ CCl₄(g)
Given ΔH° = -231.1 kJ and ΔS° = -287.6 J/K.

A) -518.7 kJ
B) -316.9 kJ
C) -145.4 kJ
D) -56.5 kJ
E) +56.5 kJ

Question 28

At 298 K,all of the following substances have a standard free energy of formation of zero EXCEPT ____.

A) Br₂(g)
B) I₂(s)
C) S₈(s)
D) Cl₂(g)
E) Hg(l)

Question 29

What is the correct form for the Gibbs-Helmholtz equation?

A) ΔG = ΔH − TΔS
B) ΔG = ΔH + TΔS
C) ΔH = ΔG − TΔS
D) ΔS = ΔH − TΔG
E) ΔG = ΔS − TΔH

Question 30

In what temperature range is ΔG° greater than zero for the formation of NH₄Cl(s)from NH₃(g)and HCl(g)? NH₃(g)+ HCl(g)→ NH₄Cl(s)
For the reaction,ΔH° = −176.0 kJ and ΔS° = −0.2845 kJ/K.

A) The temperature must be greater than 619 K.
B) The temperature must be less than 619 K.
C) The temperature must be exactly 619 K.
D) ΔG° is always greater than zero.
E) ΔG° is never greater than zero.

Question 31

Ammonia is synthesized from nitrogen and hydrogen gases at a temperature of 475°C. N₂(g)+ 3H₂(g)→ 2NH₃(g)
If ΔH° = −92.2 kJ and ΔS° = −0.1987 kJ/K,what is ΔG° for the reaction at 575°C?

A) −260.7 kJ
B) −186.6 kJ
C) −92.0 kJ
D) +2.2 kJ
E) +76.3 kJ

Question 32

At what temperatures will a reaction be spontaneous if ΔH° = +62.4 kJ and ΔS° = +301 J/K?

A) All temperatures below 207 K.
B) All temperatures above 207 K.
C) Temperatures between 179 K and 235 K.
D) The reaction will be spontaneous at any temperature.
E) The reaction will never be spontaneous.

Question 33

What is ΔG° at 555°C for a reaction with ΔH° = −152 kJ and ΔS° = 79.1 J/K?

A) −4370 kJ
B) −217 kJ
C) −196 kJ
D) +196 kJ
E) + 643 kJ

Question 34

For the decomposition of hydrogen peroxide to water and oxygen, H₂O₂(g)→ H₂O(g)+ O₂(g)
ΔH° = −106 kJ,and ΔS° = +0.0580 kJ/K.Under which of the following conditions is the reaction spontaneous (ΔG° < 0)?

A) The temperature must be greater than 1.83 × 10³ K.
B) The temperature must be less than 1.83 × 10³ K.
C) The temperature must be between 225 K and 1.83 × 10³ K.
D) ΔG° is always less than zero.
E) ΔG° is never less than zero.

Question 35

Calculate $\Delta G_{f}^{\circ}$ at 325 K for ethylene,C₂H₄(g),given the thermodynamic data below.
$\begin{array}{l}\begin{array}{lll}\text { Substance } & \Delta H_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) &S^{\circ}(\mathrm{kJ} / \mathrm{mol} \cdot \mathrm{K})\\\hline \mathrm{C}(s) & 0.0 & +0.0057 \\\mathrm{H}_{2}(g) & 0.0 & +0.1306 \\\mathrm{C}_{2} \mathrm{H}_{4}(g) & +52.3 & +0.2195\end{array}\end{array}$

A) ?47.1 kJ
B) ?19.0 kJ
C) +39.1 kJ
D) +52.1 kJ
E) +69.6 kJ

Question 36

Nitric oxide can be made from the reaction of oxygen and nitrogen gases. O₂(g)+ N₂(g)→ 2NO(g)
If ΔG° = 165.5 kJ,and ΔH° = 180.4 kJ,what is ΔS° at 325°C?

A) 0.0125 kJ/K
B) 0.0249 kJ/K
C) 0.0458 kJ/K
D) 0.142 kJ/K
E) 1.02 kJ/K

Question 37

Calculate ?S° for the dissolution of BaCl₂ in water at 25°C. BaCl₂(s)? Ba²⁺(aq)+ 2Cl?(aq)
$\begin{array}{lll}\text { Substance } & \Delta G_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) & \Delta H_{\mathrm{f}}^{0}(\mathrm{~kJ} / \mathrm{mol}) \\\hline \mathrm{BaCl}_{2}(s) & -810.4 & -858.6 \\\mathrm{Ba}^{2+}(a q) & -560.8 & -537.6 \\\mathrm{Cl}-(a q) & -131.2 & -167.2\end{array}$

A) ?0.20 kJ/K
B) ?0.14 kJ/K
C) ?0.0020 kJ/K
D) +0.12 kJ/K
E) +0.29 kJ/K

Question 38

In a gas phase reaction,what is the effect of increasing reactant or product pressure on the standard Gibbs free energy,ΔG°?

A) ΔG° increases due to decreased entropy.
B) ΔG° decreases due to decreased entropy.
C) ΔG° increases due to increased enthalpy.
D) ΔG° may either increase or decrease.
E) ΔG° is unchanged.

Question 39

When ammonium nitrate dissolves spontaneously in water the temperature of the solution decreases.Which statement is true for this system?

A) ΔH < 0 and ΔS < 0
B) ΔH < 0 and ΔS = 0
C) ΔH = 0 and ΔS > 0
D) ΔH > 0 and ΔS > 0
E) ΔH > 0 and ΔS < 0

Question 40

Calculate ?G° for the reaction below at 25.0°C.
P₄O₁₀(s)+ 6H₂O(l)? 4H₃PO₄(l)
$\begin{array}{lll}\text { Species } & \Delta H_{\mathrm{f}}^{\circ}(\mathrm{kJ} / \mathrm{mol}) & S^{\circ}(\mathrm{J} / \mathrm{mol} \cdot \mathrm{K}) \\\hline \mathrm{P}_{4} \mathrm{O}_{10}(s) & -2984.0 & 228.9 \\\mathrm{H}_{2} \mathrm{O}(l) & -285.8 & 69.95 \\\mathrm{H}_{3} \mathrm{PO}_{4}(l) & -1279.0 & 110.5\end{array}$

A) -6119.1 kJ
B) -632.8 kJ
C) -355.6 kJ
D) +210.6 kJ
E) +6119.1 kJ

Question 41

For the decomposition of calcium carbonate,ΔG° = +130.4 kJ at 25°C. CaCO₃(s)→ CaO(s)+ CO₂(g)
Calculate the partial pressure of CO₂ if ΔG = 0.0 kJ.(R = 8.31 × 10−³ kJ/K)

A) 1.3 × 10−²³ atm
B) 2.7 × 10² atm
C) 8.2 × 10−⁵ atm
D) 5.3 × 10¹ atm
E) 7.4 × 10²² atm

Question 42

Given that S(g)+ O₂(g)? SO₂(g)
?G° = -300.1 kJ
2S(g)+ 3O₂(g)? 2SO₃(g)
?G° = -742.1 kJ
Calculate $\Delta G_{f}^{\circ}$ of the following reaction:
SO₂(g)+ 1/2O₂(g)? SO₃(g)

A) -1042.2 kJ
B) -71.0 kJ
C) +2.47 kJ
D) +71.0 kJ
E) +1042.2 kJ

Question 43

For a chemical reaction,ΔG and ΔG° are equal

A) when products and reactants are in standard state concentrations.
B) when K = 0.
C) when K > 1.
D) for a system at equilibrium.
E) when the entropy change is zero.

Question 44

At 25°C,the equilibrium constant for the following reaction, Cu²⁺(aq)+ Zn(s)→ Cu(s)+ Zn²⁺(aq)
Is 1.9 × 10³⁷.Calculate ΔG° for this reaction.(R = 8.31 × 10−³ kJ/K)

A) −213 kJ
B) −145 kJ
C) −57.3 kJ
D) +57.3 kJ
E) +213 kJ

Question 45

Rubber elasticity is an entropic phenomenon.As a rubber band is stretched the entropy of the system

A) is reduced.
B) is increased.
C) remains unchanged.
D) breaks the polymer chain.
E) causes chemical bonds to form.

Question 46

If ΔG° = 0,then

A) K = 0.
B) K < 0.
C) K < 1.
D) K = 1.
E) K < −1.

Question 47

At 25°C,the acid dissociation constant for formic acid is 6.9 × 10−⁴.Calculate ΔG° for this reaction.(R = 8.31 × 10−³ kJ/K)

A) −18.0 kJ
B) −1.51 kJ
C) +1.51 kJ
D) +18.0 kJ
E) +41.4 kJ

Question 48

The standard free energy change for a chemical reaction is +13.3 kJ.What is the equilibrium constant for the reaction at 125°C? (R = 8.31 × 10−³ kJ/K)

A) 2.8 × 10^-6
B) 2.0 × 10^-5
C) 4.7 × 10^-3
D) 1.8 × 10^-2
E) 2.1 × 10²

Question 49

Given that,at 25°C, C(s)+ O₂(g)→ CO₂(g)
ΔG° = −394.4 kJ
C(s)+ O₂(g)→ CO(g)
ΔG° = −137.2 kJ
Calculate ΔG° for the reaction below.
CO(g)+ O₂(g)→ CO₂(g)

A) −531.6 kJ
B) −257.2 kJ
C) −171.5 kJ
D) +141.2 kJ
E) +531.6 kJ