Deck 18: Thermodynamics

Question 1

Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk metal from further corrosion. 4Al(s)+ 3O₂(g) $\rarr$ 2Al₂O₃(s)
Using the thermodynamic data provided below, calculate $\Delta$ S° for this reaction.

A)182.3 J/K·mol
B)131.5 J/K·mol
C)-182.3 J/K·mol
D)-626.2 J/K·mol
E)-802.9 J/K·mol

Answer 1

-626.2 J/K·mol

Question 2

Which one of the following reactions would you expect to have highest $\Delta$ S°?

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

Answer 2

C₂H₆(g)+ ⁷/₂O₂(g) $\rarr$ 2CO₂(g)+ 3H₂O(g)

Question 3

Arrange these compounds in order of increasing standard molar entropy at 25°C: C₃H₈(g), C₂H₄(g), ZnS(s), and H₂O(l).

A)ZnS(s)< H₂O(l)< C₃H₈(g)< C₂H₄(g)
B)C₂H₄(g)< H₂O(l)< C₃H₈(g)< NaCl(s)
C)ZnS(s)< C₃H₈(g)< C₂H₄(g)< H₂O(l)
D)C₃H₈(g)< C₂H₄(g)< H₂O(l)< ZnS(s)
E)ZnS(s)< H₂O(l)< C₂H₄(g)< C₃H₈(g)

Answer 3

ZnS(s)< H₂O(l)< C₂H₄(g)< C₃H₈(g)

Question 4

Calculate $\Delta$ S° at 25°C for the reduction of PbO(s), 2PbO(s)+ C(s) $\rarr$ 2Pb(s)+ CO₂(g)given these absolute entropies:

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 5

Which of these species would you expect to have the highest standard entropy (S°)?

A)CH₄(g)
B)C₂H₂(g)
C)C₂H₄(g)
D)C₂H₆(g)
E)C₃H₈(g)

Question 6

Arrange the following substances in the order of increasing entropy at 25°C. HF(g), NaF(s), SiF₄(g), SiH₄(g), Al(s)
Lowest $\rarr$ highest

A)SiF₄(g)< SiH₄(g)< NaF(s)< HF(g)< Al(s)
B)HF(g)< Al(s)< NaF(s)< SiF₄(g)< SiH₄(g)
C)Al(s)< NaF(s)< HF(g)< SiH₄(g)< SiF₄(g)
D)Al(s)< HF(g)< NaF(s)< SiF₄(g)< SiH₄(g)
E)NaF(s)< Al(s)< HF(g)< SiF₄(g)< SiH₄(g)

Question 7

Which of these species has the highest entropy (S°)at 25°C?

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

Question 8

MgCO₃(s) $\rarr$ MgO(s)+ CO₂(g)

A)1 < 2 < 3
B)2 < 3 < 1
C)3 < 2 < 1
D)2 < 1 < 3
E)1 < 3 < 2

Question 9

Which of these species would you expect to have the lowest standard entropy (S°)?

A)CH₄(g)
B)HF(g)
C)NH₃(g)
D)H₂O(g)

Question 10

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

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 11

Calculate $\Delta$ S° for the reaction SO₂(s)+ NO₂(g) $\rarr$ SO₃(g)+ NO(g).

A)53.6 J/K·mol
B)-53.6 J/K·mol
C)-22.2 J/K·mol
D)474.8 J/K·mol
E)-474.8 J/K·mol

Question 12

Determine $\Delta$ S° for the reaction SO₃(g)+ H₂O(l) $\rarr$ H₂SO₄(l).

A)169.2 J/K·mol
B)1343.2 J/K·mol
C)-169.2 J/K·mol
D)-29.4 J/K·mol
E)29.4 J/K·mol

Question 13

H₂O₂(l) $\rarr$ H₂O(l)+ ¹/₂O₂(g)

A)1 < 3 < 2
B)2 < 3 < 1
C)2 < 1 < 3
D)3 < 2 < 1
E)3 < 1 < 2

Question 14

Which of these species has the highest entropy (S°)at 25°C?

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

Question 15

Which of these species would you expect to have the lowest standard entropy (S°)?

A)Br₂(l)
B)Cl₂(g)
C)F₂(g)
D)H₂(g)
E)I₂(s)

Question 16

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)
Calculate $\Delta$ S° for this reaction using the thermodynamic data provided below.

A)-410 J/K·mol
B)-161.5 J/K·mol
C)-47.7 J/K·mol
D)21.8 J/K·mol
E)43.5 J/K·mol

Question 17

The entropy change on vaporization ( $\Delta$ S_vap)of a compound or element is

A)always negative.
B)always positive.
C)sometimes is positive and sometimes is negative.

Question 18

Mg²⁺(aq)+ 2OH^-(aq) $\rarr$ Mg(OH)₂(s)

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

Question 19

H₂O₂(l) $\rarr$ H₂O(l)+ ¹/₂O₂(g)

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

Question 20

HI has a normal boiling point of -35.4°C, and its $\Delta$ H_vap is 21.16 kJ/mol. Calculate the molar entropy of vaporization ( $\Delta$ S_vap).

A)598 J/K·mol
B)68.6 J/K·mol
C)75.2 J/K·mol
D)0.068 J/K·mol
E)89.0 J/K·mol

Question 21

At 1500°C the equilibrium constant for the reaction CO(g)+ 2H₂(g) $\rarr$ CH₃OH(g)has the value K_p = 1.4 * 10^-7. Calculate $\Delta$ G° for this reaction at 1500°C.

A)105 kJ/mol
B)1.07 kJ/mol
C)-233 kJ/mol
D)-105 kJ/mol
E)233 kJ/mol

Question 22

A negative sign for $\Delta$ G indicates that, at constant T and P,

A)the reaction is exothermic.
B)the reaction is endothermic.
C)the reaction is fast.
D)the reaction is spontaneous.
E)( $\Delta$ S) must be > 0.

Question 23

Determine the equilibrium constant K_p at 25°C for the reaction N₂(g)+ 3H₂(g) $\rarr$ 2NH₃(g) [ $\Delta$ G°_f (NH₃(g))= -16.6 kJ/mol].

A)1.52 * 10^-6
B)6.60 * 10⁵
C)8.28 * 10^-2
D)2.60
E)13.4

Question 24

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° and $\Delta$ H° for the reaction at 25°C?

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

Question 25

Sodium carbonate can be made by heating sodium bicarbonate: 2NaHCO₃(s) $\rarr$ Na₂CO₃(s)+ CO₂(g)+ H₂O(g)
Given that $\Delta$ H° = 128.9 kJ/mol and $\Delta$ G° = 33.1 kJ/mol at 25°C, above what minimum temperature will the reaction become spontaneous under standard state conditions?

A)0.4 K
B)3.9 K
C)321 K
D)401 K
E)525 K

Question 26

Calculate K_p at 298 K for the reaction SO₂(g)+ NO₂(g) $\rarr$ SO₃(g)+ NO(g).

A)6.99 * 10^-7
B)5.71 * 10^-8
C)14.2
D)475
E)1.42 * 10⁶

Question 27

The element oxygen was prepared by Joseph Priestley in 1774 by heating mercury(II)oxide: HgO(s) $\rarr$ Hg(l)+ ¹/₂O₂(g), $\Delta$ H° = 90.84 kJ/mol.
Estimate the temperature at which this reaction will become spontaneous under standard state conditions.
S°(Hg)= 76.02 J/K·mol
S°(O₂)= 205.0 J/K·mol
S°(HgO)= 70.29 J/K·mol

A)108 K
B)430 K
C)620 K
D)775 K
E)840 K

Question 28

Ozone (O₃)in the atmosphere can reaction with nitric oxide (NO): O₃(g)+ NO(g) $\rarr$ NO₂(g)+ O₂(g).
Calculate the $\Delta$ G° for this reaction at 25°C. ( $\Delta$ H° = -199 kJ/mol, $\Delta$ S° = -4.1 J/K·mol)

A)1020 kJ/mol
B)-1.22 * 10³ kJ/mol
C)2.00 * 10³ kJ/mol
D)-1.42 * 10³ kJ/mol
E)-198 kJ/mol

Question 29

Determine the equilibrium constant (K_p)at 25°C for the reaction CO(g)+ H₂O(g) $\rarr$ CO₂(g)+ H₂(g) $\Delta$ G° = -28.5 kJ/mol.

A)2.9 * 10^-60
B)1.0 * 10^-4
C)1.2
D)1.0 * 10⁵
E)3.4 * 10⁵⁹

Question 30

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

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

Question 31

For the reaction 2C(graphite)+ H₂(g) $\rarr$ C₂H₂(g), $\Delta$ G°= +209.2 kJ/mol at 25°C. If P(H₂)= 100. atm, and P(C₂H₂)= 0.10 atm, calculate $\Delta$ G for this reaction.

A)+207.8 kJ/mol
B)+226.3 kJ/mol
C)+192.1 kJ/mol
D)+17.3 kJ/mol
E)-16.9 kJ/mol

Question 32

Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk metal from further corrosion. 4Al(s)+ 3O₂(g) $\rarr$ 2Al₂O₃(s)
Calculate $\Delta$ G° for this reaction, given that $\Delta$ G°_f of aluminum oxide is -1576.4 kJ/mol.

A)-3152.8 kJ/mol
B)-1576.4 kJ/mol
C)-788.2 kJ/mol
D)1576.4 kJ/mol
E)3152.8 kJ/mol

Question 33

The equilibrium constant at 427°C for the reaction N₂(g)+ 3H₂(g) $\rarr$ 2NH₃(g)is K_p = 9.4 * 10^-5. Calculate the value of $\Delta$ G° for the reaction under these conditions.

A)-33 kJ/mol
B)-54 kJ/mol
C)54 kJ/mol
D)33 kJ/mol
E)1.3 J/mol

Question 34

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

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

Question 35

A spontaneous endothermic reaction always

A)causes the surroundings to get colder.
B)bursts into flame.
C)requires a spark to initiate it.
D)releases heat to the surroundings.

Question 36

Calculate $\Delta$ G° for the reaction 3NO₂(g)+ H₂O(l) $\rarr$ 2HNO₃(l)+ NO(g).

A)8.7 kJ/mol
B)192 kJ/mol
C)-414 kJ/mol
D)-192 kJ/mol
E)-155 kJ/mol

Question 37

For the reaction H₂(g)+ S(s) $\rarr$ H₂S(g), $\Delta$ H° = -20.2 kJ/mol and $\Delta$ S° = +43.1 J/K·mol. Which of these statements is true?

A)The reaction is only spontaneous at low temperatures.
B)The reaction is spontaneous at all temperatures.
C)( $\Delta$ G°) becomes less favorable as temperature increases.
D)The reaction is spontaneous only at high temperatures.
E)The reaction is at equilibrium at 25°C under standard conditions.

Question 38

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

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

Question 39

The equilibrium constant for the reaction AgBr(s) $\rarr$ Ag⁺(aq)+ Br^- (aq)is the solubility product constant, K_sp = 7.7* 10^-13 at 25°C. Calculate $\Delta$ G for the reaction when [Ag⁺] = 1.0 * 10^-2 M and [Br^-] = 1.0 * 10^-3 M. Is the reaction spontaneous or nonspontaneous at these concentrations?

A)( $\Delta$ G) = 69.1 kJ/mol, nonspontaneous
B)( $\Delta$ G) = -69.1 kJ/mol, spontaneous
C)( $\Delta$ G) = 97.5 kJ/mol, spontaneous
D)( $\Delta$ G) = 40.6 kJ/mol, nonspontaneous
E)( $\Delta$ G) = -97.5 kJ/mol, nonspontaneous

Question 40

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

A)- - 0
B)- + -
C)+ - +
D)+ + 0
E)- - -

Question 41

For the reaction CuS(s)+ H₂(g) $\rarr$ H₂S(g)+ Cu(s),
$\Delta$ G°_f (CuS)= -53.6 kJ/mol
$\Delta$ G°_f (H₂S)= -33.6 kJ/mol
$\Delta$ H°_f (CuS)= -53.1 kJ/mol
$\Delta$ H°_f (H₂S)= -20.6 kJ/mol
Calculate the value of the equilibrium constant (K_p)at 798 K and 1 atm pressure.

Question 42

The reaction rates of many spontaneous reactions are actually very slow. Which of these statements is the best explanation for this observation?

A)K_p for the reaction is less than one.
B)The activation energy of the reaction is large.
C)( $\Delta$ G°) for the reaction is positive.
D)Such reactions are endothermic.
E)The entropy change is negative.

Question 43

In the gas phase, methyl isocyanate (CH₃NC)isomerizes to acetonitrile (CH₃CN), H₃C-N $\equiv$ C (g) $\rarr$ H₃C-C $\equiv$ N (g)
With $\Delta$ H° = -89.5 kJ/mol and $\Delta$ G° = -73.8 kJ/mol at 25°C. Find the equilibrium constant for this reaction at 100°C.

A)1.68 * 10^-10
B)5.96 * 10⁹
C)2.16 * 10¹⁰
D)4.63 * 10^-11
E)8.64 * 10¹²

Question 44

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

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

Question 45

Find the temperature at which the reaction N₂O₄(g) $\rarr$ 2NO₂(g)will be in equilibrium when both gases are present at partial pressures of 1.00 atm.

A)300°C
B)28°C
C)55°C
D)32°C
E)562°C

Question 46

Predict the normal boiling point of triethylborane (C₆H₁₅B)using the following data:

A)92°C
B)-21°C
C)21°C
D)365°C
E)256°C

Question 47

In the gas phase, formic acid forms a dimmer, 2HCOOH(g) $\rarr$ (HCOOH)₂(g). For this reaction, $\Delta$ H° = -60.1 kJ/mol and $\Delta$ G° = -13.9 kJ/mol at 25°C. Find the equilibrium constant (K_p)for this reaction at 75 °C.

A)8960
B)273
C)0.120
D)8.33
E)1.12 * 10^-4

Question 48

Using the thermodynamic data provided below, calculate the standard change in entropy when one mole of sodium sulfate is dissolved in water? Will the solubility of sodium nitrate increase or decrease if the temperature of the system is increased?

Question 49

Which species will have the lowest absolute entropy at 25°C?

A)C₂H₅OH(l)
B)C₂H₂(g)
C)C₃H₈(g)
D)C₃H₇OH(l)
E)C₂H₆(g)

Question 50

For the reaction CuS(s)+ H₂(g) $\rarr$ H₂S(g)+ Cu(s),
$\Delta$ G°_f (CuS)= -53.6 kJ/mol
$\Delta$ G°_f (H₂S)= -33.6 kJ/mol
$\Delta$ H°_f (CuS)= -53.1 kJ/mol
$\Delta$ H°_f (H₂S)= -20.6 kJ/mol
Will this reaction proceed spontaneously at 298 K and 1 atm pressure?

Question 51

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

Question 52

Using the thermodynamic data provided below, calculate the standard change in entropy when one mole of sodium nitrate is dissolved in water? Will the solubility of sodium nitrate increase or decrease if the temperature of the system is increased?

Question 53

Find the temperature at which K_p = 42.0 for the reaction H₂(g)+ I₂(g) $\rarr$ 2HI(g). [Given: at 25°C, for H₂(g), $\Delta$ H°_f = 0, S° = 131.0 J/mol·K; for I₂(g), $\Delta$ H°_f = 62.26 kJ/mol, S° = 260.6 J/mol·K; for HI(g), $\Delta$ H°_f = 25.9 kJ/mol, S° = 206.3 J/mol·K; assume that $\Delta$ H° and $\Delta$ S° are independent of temperature.]

A)1040 K
B)168 K
C)539 K
D)1400 K
E)34,200 K

Question 54

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

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

Question 55

Find the temperature at which K_p = 4.00 for the reaction N₂O₄(g) $\rarr$ 2NO₂(g). [Given: at 25°C, for NO₂(g), $\Delta$ H°_f = 33.85 kJ/mol, S° = 240.46 J/mol·K; for N₂O₄(g), $\Delta$ H°_f = 9.66 kJ/mol, S° = 304.3 J/mol·K; assume that $\Delta$ H° and $\Delta$ S° are independent of temperature.]

A)197 °C
B)56 °C
C)36 °C
D)79 °C
E)476°C

Question 56

The solubility product constant at 25°C for AgI(s)in water has the value 8.3 * 10^-17. Calculate $\Delta$ G_rxn at 25°C for the process AgI(s) $\rarr$ Ag⁺(aq)+ I^- (aq)where [Ag⁺] = 9.1 * 10^-9 and [I^-] = 9.1 * 10^-9.

A)+4.4 kJ/mol
B)+91.7 kJ/mol
C)0.0 kJ/mol
D)-91.7 kJ/mol
E)-4.4 kJ/mol

Question 57

For the reaction CuS(s)+ H₂(g) $\rarr$ H₂S(g)+ Cu(s),
$\Delta$ G°_f (CuS)= -53.6 kJ/mol
$\Delta$ G°_f (H₂S)= -33.6 kJ/mol
$\Delta$ H°_f (CuS)= -53.1 kJ/mol
$\Delta$ H°_f (H₂S)= -20.6 kJ/mol
Calculate $\Delta$ G at 798 K and 1 atm pressure (assume $\Delta$ S° and $\Delta$ H° do not change with temperature).

Question 58

A sample of solid naphthalene is introduced into an evacuated flask. Use the data below to calculate the equilibrium vapor pressure of naphthalene (C₁₀H₈)in the flask at 35°C.

A)890. mmHg
B)0.21 mmHg
C)696 mmHg
D)0.086 mmHg
E)833 mmHg

Question 59

Which species will have the greatest absolute entropy at 25°C?

A)Ne(g)
B)C₂H₂(g)
C)H₂O(l)
D)C₂H₅OH(l)
E)C₄H₁₀(g)

Question 60

Calculate $\Delta$ G° for the combustion of ethanol vapor, C₂H₅OH(g), at 750°C in oxygen to form carbon dioxide and water vapor. The following data is valid at 25°C:

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

Question 61

For the reaction 3H₂(g)+ N₂(g) $\rarr$ 2NH₃(g), K_c = 9.0 at 350°C. What is the value of $\Delta$ G at this temperature when 1.0 mol NH₃, 5.0 mol N₂, and 5.0 mol H₂ are mixed in a 2.5 L reactor?

Question 62

Is the reaction SiO₂(s)+ Pb(s) $\rarr$ PbO₂(s)+ Si(s)spontaneous?
$\Delta$ G°_f (PbO₂)= -217 kJ/mol
$\Delta$ G°_f (SiO₂)= -856 kJ/mol

Question 63

Predict the sign of $\Delta$ S for the process Ni(s, 50°C) $\rarr$ Ni(s, 25°C).

Question 64

Assuming $\Delta$ S° and $\Delta$ H° do not vary with temperature, at what temperature will the reaction shown below become spontaneous?
C(s)+ H₂O(g) $\rarr$ H₂(g)+ CO(s)( $\Delta$ S° = 133.6 J/K·mol; $\Delta$ H° = 131.3 kJ/mol)

Question 65

Predict the sign of $\Delta$ S for the reaction O₂(g) $\rarr$ 2O(g).

Question 66

For the reaction SbCl₅(g) $\rarr$ SbCl₃(g)+ Cl₂(g),
$\Delta$ G°_f (SbCl₅)= -334.34 kJ/mol
$\Delta$ G°_f (SbCl₃)= -301.25 kJ/mol
$\Delta$ H°_f (SbCl₅)= -394.34 kJ/mol
$\Delta$ H°_f (SbCl₃)= -313.80 kJ/mol
Calculate $\Delta$ G at 800 K and 1 atm pressure (assume $\Delta$ S° and $\Delta$ H° do not change with temperature).

Question 67

For the reaction SbCl₅(g) $\rarr$ SbCl₃(g)+ Cl₂(g),
$\Delta$ G°_f (SbCl₅)= -334.34 kJ/mol
$\Delta$ G°_f (SbCl₃)= -301.25 kJ/mol
$\Delta$ H°_f (SbCl₅)= -394.34 kJ/mol
$\Delta$ H°_f (SbCl₃)= -313.80 kJ/mol
Calculate the value of the equilibrium constant (K_p)at 800 K and 1 atm pressure.

Question 68

For the reaction SbCl₅(g) $\rarr$ SbCl₃(g)+ Cl₂(g),
$\Delta$ G°_f (SbCl₅)= -334.34 kJ/mol
$\Delta$ G°_f (SbCl₃)= -301.25 kJ/mol
$\Delta$ H°_f (SbCl₅)= -394.34 kJ/mol
$\Delta$ H°_f (SbCl₃)= -313.80 kJ/mol
Calculate the value of the equilibrium constant (K_p)for this reaction at 298 K.

Question 69

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

Question 70

What is the free energy change for the reaction SiO₂(s)+ Pb(s) $\rarr$ PbO₂(s)+ Si(s)?
$\Delta$ G°_f (PbO₂)= -217 kJ/mol
$\Delta$ G°_f (SiO₂)= -856 kJ/mol

Question 71

Rubidium has a heat of vaporization of 69.0 kJ/mol at its boiling point (686°C). Calculate $\Delta$ S for this process, Rb(l) $\rarr$ Rb(g), at 1 atm and 686°C.

Question 72

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

Question 73

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

Question 74

The heat of vaporization of water is 2.27 kJ/g. What is $\Delta$ S_vap per mole at the normal boiling point?

Question 75

Predict the sign of $\Delta$ S for the process N₂(g, 10 atm) $\rarr$ N₂(g, 1atm).

Question 76

For the reaction 3H₂(g)+ N₂(g) $\rarr$ 2NH₃(g), K_c = 9.0 at 350°C. In what direction does this reaction proceed at 350°C under standard state conditions?

Question 77

For the reaction SbCl₅(g) $\rarr$ SbCl₃(g)+ Cl₂(g),
$\Delta$ G°_f (SbCl₅)= -334.34 kJ/mol
$\Delta$ G°_f (SbCl₃)= -301.25 kJ/mol
$\Delta$ H°_f (SbCl₅)= -394.34 kJ/mol
$\Delta$ H°_f (SbCl₃)= -313.80 kJ/mol
Will this reaction proceed spontaneously at 298 K and 1 atm pressure?

Question 78

Predict the sign of $\Delta$ S for the reaction 6CO₂(g)+ 6H₂O(g) $\rarr$ C₆H₁₂O₆(g)+ 6O₂(g).

Question 79

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

Question 80

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) $\rarr$ 2NO(g)at this temperature.