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SAT Papers: Chemistry MCQ: Thermodynamics Part-II

Thermodynamics

1. For a process at 451 K and constant pressure, Ssurr is -326 J K-1. Calculate the quantityof heat (in kJ) absorbed by the system.

2. Which of the following produces an INCREASE in entropy of the system?a. H2O(l) --> H2O(s)b. 2O2(g) + 2SO(g) --> 2SO3(g)c. 2CH3OH(g) + 3O2(g) --> 2CO2(g) + 4H2O(l)d. I2(s) --> I2(l)e. None of the above.

3. The gas-phase reaction between H2 and Cl2 can be initiated by ultraviolet light at 25oC,H2(g) + Cl2(g) --> 2HCl(g)

Using the thermodynamic data provided below, calculate the standard free energy change

(in kJ) at 25oC for this reaction.

compound Hfo, kJ mol

-1 S

o, J mol

-1K

-1

H2 0 130.57

Cl2 0 222.96

HCl -92.307 186.80

4. In lecture, you observed the following reaction,2H2(g) + O2(g) --> 2H2O(g)

For this reaction, Ho = -241.8 kJ and So = -88.8 J K-1. Assuming that Ho = H and

So = S at all temperatures, calculate the temperature (in K) at which this reaction

would become non-spontaneous.

5. For a particular chemical reaction at 400oC, G = -67 kJ. Calculate the time (in seconds)it will take for the reaction to reach completion.

6.

For a particular chemical reaction, H

o

is positive and S

o

is negative. Which of thefollowing statements about the spontaneity of the reaction under standard conditions is

TRUE?

a. The reaction will be spontaneous only if the magnitude of Ho is large enough toovercome the unfavorable entropy change.

b. The reaction will be spontaneous only if the magnitude of So is large enough toovercome the unfavorable enthalpy change.

c. The reaction will be spontaneous regardless of the magnitudes of Ho and So.

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d. The reaction cannot be spontaneous.e. The reaction will be spontaneous only of Go is positive.

7. Which of the following is TRUE for an operating voltaic cell?a. G > 0 ; E = 0b.

G < 0 ; E < 0c. G = 0 ; E > 0

d. G = 0 ; E = 0e. G < 0 ; E > 0

8. Which of the following produces a DECREASE in entropy of the system?Hint: thesystem is shown in bold.

a. Dissolving sugar in a cup of coffee.b. Condensation ofwater on the surface of a glass of iced tea on a hot summer day.c. Boiling water in a pot on the stove to make spaghetti.d. Allowing the liquid propane in a gas grill to escape from the tank.e.

Producing CO2 gas from baking soda (NaHCO3) when baking a cake.9. Consider the following reaction and thermodynamic data,

2H2O2(aq) 2H2O(l) + O2(g)

substance Hfo, kJ mol

-1 S

o, J mol

-1K

-1

H2O2(aq) -191.17 143.9

H2O(l) -285.83 69.91

O2(g) 0 205.14

Calculate the value (in kJ) of Go at 25oC.

10.For a particular chemical reaction, both Ho and So are negative. Which of thefollowing statements about the spontaneity of the reaction under standard conditions is

TRUE?

a. The reaction will be spontaneous only if the magnitude of Ho is large enough toovercome the unfavorable entropy change.

b. The reaction will be spontaneous only if the magnitude of So is large enough toovercome the unfavorable enthalpy change.

c. The reaction will be spontaneous regardless of the magnitudes of Ho and So.d. The reaction cannot be spontaneous.e. The reaction will be spontaneous only of Go is positive.

11.The boiling point of a substance is the temperature at which equilibrium is establishedbetween the liquid and the vapor.

CH3CH2OH(l) CH3CH2OH(g)

Calculate the boiling point (in K) of ethanol, CH3CH2OH, if H = 42.6 kJ and S = 122J/K for this process.

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12.What is the significance of the Third Law of Thermodynamics? Choose the best answer.a. The absolute entropy of a substance decreases with increasing temperature.b. The change in entropy of the universe must be positive for a spontaneous process.c. The absolute value of entropy can be measured for some very pure substances.d. The change in entropy of the universe equals the sum of the change in entropy of

the system plus the change in entropy of the surroundings.e. The entropy of the universe is constant.13.The Ksp for the sparingly soluble salt barium chromate (BaCrO4) at 25oC is equal to 2.0 x

10-10. Calculate Go (in kJ) for the following reaction.

BaCrO4(s) Ba2+

(aq) + CrO42-

(aq)

14.A Chemistry 116student determined the value of Ksp for a saturated solution of borax atseveral different temperatures. The value for S

ofor the dissolution of borax in water

can be determined from:

a. the slope of the line resulting from a plot of ln Ksp versus (1/T).b.

the y-intercept of the line resulting from a plot of ln Ksp versus T.c. the slope of the line resulting from a plot of Ksp versus (1/T).

d. the y-intercept of the line resulting from a plot of ln Ksp versus (1/T).e. the slope of the curve at 25oC from a plot of ln Ksp versus T.

15.Consider the following gas-phase reaction,2NO2(g) 2NO(g) + O2(g), G

o= +70.5 kJ

If 1.00 mole of NO2(g) is placed in a 1.00-L flask (no NO(g) or O2(g) initially) at 25oC,

which of the following statements is TRUE?

a.

The reaction will occur spontaneously from left to right.b. The reaction will occur spontaneously from right to left.c. The reaction is not spontaneous in either direction.d. The reaction is spontaneous in both directions.e. At equilibrium, the concentrations of NO(g) and O2(g) will be much larger than

the concentration of NO2(g).16.For which one of the following reactions does the entropy of the system INCREASE?

a. NH3(g) + HCl(g) --> NH4Cl(s)b. Ag+(aq) + Cl-(aq) --> AgCl(s)c. 2H2(g) + O2(g) --> 2H2O(g)d.

NH3(g) + H2O(l) --> NH4

+

(aq) + OH

-

(aq)e. 2H2O2(l) --> 2H2O(l) + O2(g)17.Consider the following characteristics of chemical reactions,

I. spontaneityII. maximum amount of work that can be done

III. speed

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The value of G for a chemical reaction under a given set of conditions providesinformation about:

d. I onlye. II onlyf.

III onlyg. I and II

h. I, II and III18.Consider the following standard reduction potentials,

half-reaction Eo, V

I3-(aq) + 2e- --> 3I-(aq) 0.53

Cr3+

(aq) + e---> Cr

2+(aq) -0.41

19.Calculate Go (in kJ) for the following reaction at 25oC.20.Cr

2+

(aq) + I3-

(aq) --> Cr3+

(aq) + I-

(aq)21.Consider the following reaction,

2SO2(g) + O2(g) 2SO3(g)

and the following thermochemical data,

substance Gfo, kJ/mol

SO2(g) -300.194

O2(g) 0.0

SO3(g) -371.06

Calculate the value of the equilibrium constant for this reaction at 25oC.

22.For the dissociation of acetic acid in water at 25oC,CH3COOH(l) + H2O(l) H3O

+(aq) + CH3COO

-(aq)

Ho

= 284.3 kJ and So

= -143.1 J K-1

. Calculate the value of Go

(in kJ) for thisreaction at equilibrium.

23.Consider the carbonylation (i.e., addition of CO) of methanol, CH3OH, to produce aceticacid, CH3COOH, in a closed system at constant temperature and pressure,

CH3OH(g) + CO(g) CH3COOH(g)

and the following data:

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substance Hfo, kJ mol

-1 So, J mol

-1K

-1

CH3OH(g) -201 240

CO(g) -110 198

CH3COOH(g) -432 283

If the initial concentration of CH3OH(g) is 1.5 M and the initial concentration of CO(g) is

2.0 M, what is the concentration (in M) of CH3OH(g) at equilibrium, at 298 K?

24.For which of the following processes does the entropy of the system DECREASE?a. Melting of ice.b. Dissolving table salt in water.c. Decomposition of liquid hydrogen peroxide to produce liquid water and oxygen

gas.

d. Precipitation of silver chloride from a solution containing silver ions and chlorideions.

e. The entropy of the system increases in all of the above processes.25.For a particular chemical reaction, the values for H and S are both positive. Which of

the following statements is TRUE about this reaction?

a. The reaction is spontaneous at any temperature.b. The reaction is not spontaneous at any temperature.c. The reaction is spontaneous when the temperature is high enough to overcome

H.

d. The reaction is spontaneous when the temperature is low enough to overcomeH.

e. The reaction is spontaneous when the temperature is low enough to overcomeS.

26.For the boiling of methanol,CH3OH(l) --> CH3OH(g)

Ho

= +38.0 kJ, and So

= +113.0 J/K. Assume that methanol boils at a temperature at

which the value of G is equal to zero. Using the values of Ho

and So, calculate the

temperature (in K) at which methanol boils.

27.Which of the following reactions is unfavorable at low temperatures but becomesfavorable as the temperature increases?

a. 2 CO(g) + O2(g) --> CO2(g); Ho = -566 kJ; So = -173 J/Kb. 2 H2O(g) --> 2 H2(g) + O2(g); Ho = 484 kJ; So = 90.0 J/Kc. 2 N2O(g) --> 2 N2(g) + O2(g); Ho = -164 kJ; So = 149 J/Kd. PbCl2(s) --> Pb2+(aq) + O2(g); Ho = 23.4 kJ; So = -12.5 J/K

28.The following reaction is spontaneous as written:Zn(s) + Cu

2+(aq) --> Zn

2+(aq) + Cu(s)

Which of the following statements is TRUE?

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a. Keq > 1 and Go = 0b. Keq > 1 and Go < 0c. Keq < 1 and Go < 0d. Keq > 1 and Go > 0e. Keq < 1 and Go = 0

29.A spontaneous reaction ALWAYS occurs when:a. Ho < 0 and So < 0

b. Ho > 0 and So < 0c. Ho < 0 and So > 0d. Ho > 0 and So = 0e. Ho > 0 and So > 0

30.When a reaction is at equilibrium, which of the following statements is TRUE?a. G = Gob. ln Keq = 0c. Go = 0d. Q = 0e.

G = 031.For mercury the molar entropy of vaporization is 92.92 J K -1 mol-1 and the molar

enthalpy of vaporization is 58.51 kJ mol -1. Therefore, the normal boiling point of mercury

inoC is:

a. 273oCb. 357oCc. 516oCd. 670oCe. unable to determine unless G of vaporization is known.

32.Which statement is TRUE for an operating electrolytic cell?a. G > 0 and Ecell < 0b.

G = 0 and Ecell > 0c. G < 0 and Ecell = 0

d. G = 0 and Ecell = 0e. G > 0 and Ecell > 0

33.For which ONE of the following reactions does the entropy of the system DECREASE?a. NH4NO3 (s) -> NH4+ (aq) + NO3- (aq)b. 2 H2O2 (l) -> 2 H2O (l) + O2 (g)c. Ba(OH)2.8H2O (s) + 2 NH4SCN (s) -> Ba(SCN)2 (aq) + 2 NH3 (aq) + 10 H2O (l)d. NO (g) + NO2 (g) -> N2O3 (g)e. CO2 (s) -> CO2 (g)

34.For a particular chemical reaction at 25oC, H = -432 kJ. Which of the followingstatements is TRUE?

a. The reaction will be spontaneous, at any temperature, if S is positive.b. The reaction will be spontaneous, at any temperature, if S is negative.c. The reaction will be spontaneous only if G is positive.d. The reaction can never be spontaneous, at any temperature.e. There is insufficient information provided to answer this question.

35.For a particular chemical reaction, Ho = +60.0 kJ and So = +121 J/K. At whattemperature (in K) would this reaction become spontaneous?

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36.Consider the gas-phase hydrogenation of ethylene, C2H2, to produce ethane, C2H6,C2H2 (g) + 2 H2 (g) -> C2H6 (g)

and the following thermodynamic data:

substance Hfo, kJ mol

-1 So, J mol

-1K

-1

C2H2(g) 227.0 201.0

H2(g) 0 131.0

C2H6(g) -84.70 229.5

Under standard conditions, which of the following statements is TRUE?

a. The reaction is spontaneous; Ho is favorable while So is not.b. The reaction is spontaneous; So is favorable while Ho is not.c. The reaction is not spontaneous; So is favorable while Ho is not.d. The reaction is not spontaneous; Ho is favorable while So is not.e. The reaction is not spontaneous; neither Ho nor So are favorable.

37.Consider the gas-phase reaction of hydrogen, H2, and oxygen, O2, to produce water,2 H2 (g) + O2 (g) -> 2 H2O (g)

and the following thermodynamic data:

substance Gfo, kJ/mol

H2(g) 0O2(g) 0

H2O(g) -228.6

Calculate the value of the equilibrium constant for this reaction under standard

conditions.

38.Consider the gas-phase reaction of hydrogen, H2, with carbon monoxide, CO, to formformaldehyde, H2CO, in a closed system at constant pressure,

H2 (g) + CO (g) -> H2CO (g)

and the following thermodynamic data,

substance Hfo, kJ mol

-1 So, J mol-1 K-1

H2(g) 0 131

CO(g) -110 198

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H2CO(g) -116 219

If the initial concentration of CO (g) is 1.5 M and the initial concentration of H 2 (g) is 2.3M, calculate the concentration (in M) of H2CO (g) at equilibrium, at 298 K.

39.For a certain process, S(system) > 0 and S(surroundings) > 0. The process:a. is spontaneous.b. is exothermic.c. decreases the entropy of the universe.d. is endothermic.e. is at equilibrium.

40.In which case does the spontaneity of a reaction depend on the temperature?a. H = 0 and S < 0b. H > 0 and S > 0c. H < 0 and S = 0d. H > 0 and S = 0e. H < 0 and S > 0

41.Consider the following reaction:H2O(g) + Cl2O(g) 2 HOCl(g)

For this reaction, Keq = 0.090 at 25oC. Calculate the value (in kJ/mol) of Go for this

reaction.

42.For a particular process at 500 K, G = -3.0 kJ and H = -23.0 kJ. If the process iscarried out reversibly, caluclate the amount (in kJ) of useful work that can be performed.

43.Which of the following statements concerning the change in Go and G during achemical reaction is most correct?

a. Go remains constant while G changes and becomes equal to Go atequilibrium.

b. Both Go and G remain constant during a chemical reaction.c. Initially both G and Go are equal to zero. The value of Go changes to a

value determined by the equilibrium constant; the value of G peaks and thendecreases to zero at equilibrium.

d. Go remains constant if the reaction is carried out under standard conditions;G remains constant if the reaction is carried out under non-standard conditions.

e. Go remains constant while G changes and becomes equal to zero atequilibrium.

44.The enthalpy of vaporization of ethanol is 38.7 kJ/mol at its boiling point of 78 oC.Calculate the change in entropy (in J/mol) of the surroundings when 1.00 mole of ethanolis vaporized at 78oC and 1.00 atm of pressure.

45.A certain chemical reaction carried out at constant temperature and pressure has S > 0.What can you conclude about the spontaneity of this reaction?

a. The reaction is not spontaneous if it is endothermic and the temperature issufficiently high.

b. The reaction is not spontaneous at any temperature.

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c. The reaction is not spontaneous if it is exothermic and the temperature issufficiently low.

d. The reaction is only spontaneous at high temperatures.e. The reaction is spontaneous if it is exothermic and the temperature is sufficiently

high.

46.Consider the following reaction:

2 C(graphite) + H2(g) --> C2H2(g)

Go

= 209.2 kJ at 25oC, P(H2) = 100 atm, P(C2H2) = 0.10 atm

Calculate the value (in kJ) of G for this reaction.

47.We observed that when two white crystalline substances were mixed the beaker froze tothe wooden board it was sitting on. The reaction is as follows:

Ba(OH)2:8H2O(s) + 2 NH4NO3(s) --> Ba(NO3)2(aq) + 2 NH3(g) + 10 H2O(l)

For this reaction, Ho = 170.44 kJ and So = 657.4 J/K. Which of the followingstatements must be TRUE about the process?

a. Enthalpy is favorable and entropy is unfavorable.b. Neither entropy nor entropy are favorable.c. Both enthalpy and entropy are favorable.d. Enthalpy is unfavorable and entropy is favorable.e. The process is not spontaneous because it had to be stirred.

1.