Deck 10: Spontaneity, Entropy, and Free Energy

Question 1

A gas expands isothermally and irreversibly.
ΔS is

A) less than zero.
B) More information is needed.
C) greater than zero.
D) equal to zero.

Answer 1

greater than zero.

Question 2

In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C.
Calculate ΔT.

A) 25°C
B) 100°C
C) 0°C
D) 48°C
E) none of these

Answer 2

0°C

Question 3

A gas expands isothermally and irreversibly.
ΔE is

A) greater than zero.
B) less than zero.
C) equal to zero.
D) More information is needed.

Answer 3

equal to zero.

Question 4

One mole of an ideal gas is compressed isothermally and reversibly at 607.4 K from 5.60 atm to 8.90 atm.
Calculate ΔH.

A) 2.34 kJ
B) -2.34 kJ
C) 0 kJ
D) 3.85 kJ
E) none of these

Question 5

A gas expands isothermally and irreversibly.
q is

A) More information is needed.
B) less than zero.
C) greater than zero.
D) equal to zero.

Question 6

Consider the dissociation reaction of the acid HF. Why is ΔS negative?

A) The reaction is expected to be exothermic, and ΔS thus should be negative.
B) The reaction is expected to be endothermic, and thus ΔS should be negative.
C) Each HF molecule produces two ions when it dissociates.
D) The ions are hydrated.
E) none of these

Question 7

Consider the process A(l) A(s). Which direction favors positional randomness?

A) to the left
B) neither
C) It depends on the temperature.
D) to the right

Question 8

A gas expands isothermally and irreversibly.
ΔH is

A) less than zero.
B) More information is needed.
C) equal to zero.
D) greater than zero.

Question 9

One mole of an ideal gas expands isothermally and reversibly at 0°C. The pressure on 1 mol of an ideal monatomic gas changes from 100.0 atm to 1.00 atm.
Calculate q.

A) -225 kJ
B) 0
C) -10.5 kJ
D) 10.5 kJ
E) 225 kJ

Question 10

A gas expands isothermally and irreversibly.
ΔG is

A) More information is needed.
B) less than zero.
C) greater than zero.
D) equal to zero.

Question 11

One mole of an ideal gas is compressed isothermally and reversibly at 607.4 K from 5.60 atm to 8.90 atm.
Calculate w.

A) -298 kJ
B) 2.34 kJ
C) 298 kJ
D) -2.34 kJ
E) none of these

Question 12

Consider the process A(l) A(s). An increase in temperature favors which direction?

A) to the right
B) to the left
C) More information is needed.
D) neither

Question 13

A gas expands isothermally and irreversibly.
w is

A) less than zero.
B) greater than zero.
C) More information is needed.
D) equal to zero.

Question 14

One mole of an ideal gas expands isothermally and reversibly at 0°C. The pressure on 1 mol of an ideal monatomic gas changes from 100.0 atm to 1.00 atm.
Calculate w.

A) 10.5 kJ
B) 225 kJ
C) -10.5 kJ
D) 0
E) -225 kJ

Question 15

Which of the following result(s) in an increase in the entropy of the system? I. (See diagram.)
II. Br₂(g) → Br₂(l)
III. NaBr(s) → Na⁺(aq) + Br^-(aq)
IV. O₂(298 K) → O₂(373 K)
V. NH₃(1 atm, 298 K) → NH₃(3 atm, 298 K)

A) I, III, IV
B) I, II, III, IV
C) I
D) II, V
E) I, II, III, V

Question 16

One mole of an ideal gas is compressed isothermally and reversibly at 607.4 K from 5.60 atm to 8.90 atm.
Calculate q.

A) 298 kJ
B) -298 kJ
C) 2.34 kJ
D) -2.34 kJ
E) none of these

Question 17

In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C.
Calculate ΔV.

A) -5.87 L
B) 6.11 L
C) -6.11 L
D) 5.87 L
E) none of these

Question 18

A mixture of hydrogen and chlorine remains unreacted until it is exposed to ultraviolet light from a burning magnesium strip. Then the following reaction occurs very rapidly. Select the statement below that best explains this behavior.

A) The reactants are thermodynamically more stable than the products.
B) The reaction is spontaneous, but the reactants are kinetically stable.
C) The reaction has a small equilibrium constant.
D) The ultraviolet light raises the temperature of the system and makes the reaction more favorable.
E) The negative value for ΔS slows down the reaction.

Question 19

A gas expands isothermally and irreversibly.
ΔS_surr is

A) More information is needed.
B) equal to zero.
C) less than zero.
D) greater than zero.

Question 20

One mole of an ideal gas is compressed isothermally at 607.4 K from 5.60 atm to 8.90 atm. If the process is carried out in two irreversible steps (intermediate step at P = 7.00 atm), calculate the following.ΔS

A) 0 J/K
B) -3.85 J/K
C) 3.85 J/K
D) -2.34 J/K
E) 2.34 J/K

Question 21

1.8 mol of an ideal gas at 303 K is compressed isothermally and reversibly from 2.2 L to 0.20 L. What is ΔS?

A) -10.9 kJ/K
B) 36 J/K
C) -36 J/K
D) -18 J/K
E) -20 J/K

Question 22

Which statement is true?

A) There is always more heat given off to the surroundings in a reversible process than in an unharnessed one.
B) In a reversible process, the state functions of the system are always much greater than those of the surroundings.
C) A thermodynamically reversible process takes place infinitely fast.
D) All real processes are irreversible.
E) All these statements are true.

Question 23

In a certain reversible expansion, a system at 300. K absorbs exactly 6.00 × 10² J of heat. In the irreversible recompression to the original state of the system, twice as much work is done on the system as is performed on the surroundings in the expansion. What is the entropy change of the system in the recompression step?

A) 0.00 J/K
B) 2.00 J/K
C) -4.00 J/K
D) -2.00 J/K
E) 4.00 J/K

Question 24

At 1 atm, a liquid is heated above its normal boiling point.
ΔS_univ for this process is

A) equal to zero.
B) less than zero.
C) greater than zero.
D) cannot be determined

Question 25

A machine employs the isothermal expansion of 1 mol of an ideal gas from 4.50 L to 15.0 L. At 25°C, the machine performs 3.00 kJ of work. What percent of the maximum possible work is the machine producing?

A) 15.0%
B) 50.3%
C) This amount of work cannot be correct.
D) 0.60%
E) 4.50%

Question 26

If the change in entropy of the surroundings for a process at 443 K and constant pressure is -347 J/K, what is the heat flow absorbed by the system?

A) 154 kJ
B) 783 kJ
C) -154 kJ
D) -18.5 kJ
E) 18.5 kJ

Question 27

Which of the following is true?

A) For any process, ΔS_surr and ΔS_sys have opposite signs.
B) As long as the disorder of the surroundings is increasing, a process will be spontaneous.
C) If ΔS_surr = -ΔS_sys , the process is at equilibrium.
D) ΔH° is zero for a chemical reaction at constant temperature.
E) none of these

Question 28

One mole of an ideal gas at 25°C is expanded isothermally and reversibly from 125.0 L to 250.0 L. Which statement is correct?

A) ΔS_gas = ΔS_surr
B) ΔS_gas = Rln2
C) ΔS_gas = 0
D) ΔS_univ = 0
E) ΔS_surr = 0

Question 29

Calculate the entropy change when 5.00 mol of a monatomic ideal gas is cooled from 135°C to 85°C at 1 atm.

A) -48.9 J/K
B) -13.6 J/K
C) -250.0 J/K
D) -9.62 J/K
E) -2.74 J/K

Question 30

ΔS_surr is _______ for exothermic reactions and ______ for endothermic reactions.

A) favorable, unfavorable
B) favorable, favorable
C) unfavorable, favorable
D) unfavorable, unfavorable
E) cannot tell

Question 31

ΔS is _______ for exothermic reactions and ______ for endothermic reactions.

A) unfavorable, unfavorable
B) favorable, unfavorable
C) favorable, favorable
D) unfavorable, favorable
E) cannot tell

Question 32

In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C.
Calculate w.

A) 0
B) 23.5 kJ
C) 59.5 kJ
D) -59.5 kJ
E) -23.5 kJ

Question 33

One mole of an ideal gas is compressed isothermally and reversibly at 607.4 K from 5.60 atm to 8.90 atm.Calculate ΔS.

A) 0
B) 3.85 J/K
C) 2.34 J/K
D) -2.34 J/K
E) -3.85 J/K

Question 34

In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C.Calculate ΔE.

A) 0 kJ
B) 119 kJ
C) 59.5 kJ
D) -59.5 kJ
E) none of these

Question 35

One mole of an ideal gas at 25°C is expanded isothermally from 5.0 L to 10.0 L under such conditions that no work is produced in the surroundings. Which statement is correct?

A) ΔS_gas = 0
B) ΔS_gas = Rln2/298
C) ΔS_surr = 0
D) ΔS_univ = 0
E) ΔS_gas = ΔS_surr

Question 36

Calculate ΔG for the isothermal compression of 1 mol of an ideal monatomic gas from 1.4 atm to 5.0 atm at 25°C.

A) 1.5 × 10³ J
B) 3.2 × 10³ J
C) 4.7 × 10³ J
D) -3.2 × 10³ J
E) -1.5 × 10³ J

Question 37

At 1 atm, a liquid is heated above its normal boiling point.
ΔS for this process is

A) greater than zero.
B) less than zero.
C) equal to zero.
D) cannot be determined

Question 38

One mole of an ideal gas expands isothermally and reversibly at 0°C. The pressure on 1 mol of an ideal monatomic gas changes from 100.0 atm to 1.00 atm.Calculate ΔE.

A) 450 kJ
B) -21.0 kJ
C) -450 kJ
D) 21.0 kJ
E) none of these

Question 39

At 1 atm, a liquid is heated above its normal boiling point.
ΔS_surr for this process is

A) less than zero.
B) cannot be determined
C) greater than zero.
D) equal to zero.

Question 40

A rigid insulated box contains 20.0 g of He(g) at 25.0° C and 1.00 atm in one compartment and 20.0 g of N₂(g) at 115° C and 2.00 atm in the other compartment. These compartments are connected by a partition that transmits heat. What is the final temperature in the box at thermal equilibrium? (C_v(He) = 12.5 J/K•mol; C_v(N₂) = 20.7 J/K•mol)

A) 81.0°C
B) 70.0°C
C) 58.9°C
D) 42.3°C
E) none of these

Question 41

In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C.
Calculate ΔS.

A) -20.5 J/K
B) -26.8 J/K
C) 26.8 J/K
D) 20.5 J/K
E) none of these

Question 42

Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423°C). For the process X(l) → X(g) at 1 atm and 423°C, calculate the value of:
ΔG

A) 79.6 J/K•mol
B) -79.6 J/K•mol
C) 0
D) 103 J/K•mol
E) -103 J/K•mol

Question 43

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
What is ΔS?

A) More information is needed.
B) less than zero
C) equal to zero
D) greater than zero

Question 44

Choose the correct statement.

A) A reaction that exhibits a negative value of ΔS cannot be spontaneous.
B) Exothermic reactions are always spontaneous.
C) Free energy is independent of temperature.
D) At constant pressure and temperature, a decrease in free energy ensures an increase in the entropy of the system.
E) none of these

Question 45

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
Calculate the minimum work required to compress 1.9 mol of an ideal monatomic gas from 48.0 L to 17.8 L at 29°C.

A) 7.1 × 10³ J
B) 4.5 × 10² J
C) 4.7 × 10³ J
D) -7.1 × 10³ J
E) 2.5 × 10² J

Question 46

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
6.00 mol of a monatomic ideal gas is cooled from 254°C to 24°C at constant volume. Calculate ΔS.

A) -31.1 J/K
B) -42.9 J/K
C) -1.77 × 10² J/K
D) -18.6 J/K
E) -71.5 J/K

Question 47

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
Calculate ΔS for cooling 2.60 mol of an ideal monatomic gas from 88°C to 39°C at constant volume.

A) -1.82 J/K
B) -17.6 J/K
C) -3.15 J/K
D) -4.73 J/K
E) -26.4 J/K

Question 48

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
What is q?

A) greater than zero
B) More information is needed.
C) equal to zero
D) less than zero

Question 49

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
Calculate ΔS for an isothermal (95°C) expansion of 2 mol of a monatomic ideal gas from 100.0 atm to 1.00 atm.

A) -38.3 J/K
B) 38.3 J/K
C) -76.6 J/K
D) 76.6 J/K
E) none

Question 50

Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423°C). For the process X(l) → X(g) at 1 atm and 423°C, calculate the value of:
ΔS_surr

A) -79.6 J/K•mol
B) 0
C) -103 J/K•mol
D) 103 J/K•mol
E) 79.6 J/K•mol

Question 51

In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C.
Calculate ΔG.

A) -7.98 kJ
B) 7.98 kJ
C) 0 kJ
D) 59.5 kJ
E) none of these

Question 52

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
What is ΔH?

A) less than zero
B) More information is needed.
C) greater than zero
D) equal to zero

Question 53

When a gas is expanded isothermally and reversibly at 39°C, the work done is -43.4 kJ. Calculate ΔS.

A) 1.11 kJ/K
B) -1113 J/K
C) -1156 J/K
D) -1.11 kJ/K
E) 1.39 × 10² J/K

Question 54

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
Calculate ΔS for cooling 2.1 mol of an ideal monatomic gas from 81°C to 44°C at constant pressure.

A) -26.6 J/K
B) -2.89 J/K
C) -4.82 J/K
D) -2.29 J/K
E) -1.93 J/K

Question 55

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
What is ΔG?

A) less than zero
B) equal to zero
C) greater than zero
D) More information is needed.

Question 56

Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423°C). For the process X(l) → X(g) at 1 atm and 423°C, calculate the value of:
ΔS_univ

A) 0
B) -79.6 J/K•mol
C) 79.6 J/K•mol
D) -103 J/K•mol
E) 103 J/K•mol

Question 57

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
What is w?

A) greater than zero
B) More information is needed.
C) equal to zero
D) less than zero

Question 58

A 100-mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an ionic solid is added, the temperature decreases from 21.5°C to 20.8°C as the solid dissolves. Which of the following is true for the dissolving of the solid?

A) ΔH < 0
B) ΔS_sys< 0
C) ΔS_univ > 0
D) ΔS_surr > 0
E) none of these

Question 59

For which process is ΔS negative?

A) evaporation of 1 mol of CCl₄(l)
B) grinding a large crystal of KCl to powder
C) raising the temperature of 100 g of Cu from 275 K to 295 K
D) mixing 5 mL of ethanol with 25 mL of water
E) compressing 1 mol of Ne at constant temperature from 1.5 atm to 0.5 atm

Question 60

The process H₂O(g) → H₂O(l) takes place at 1 atm and 95°C.
Assume that the enthalpy of fusion of ice is 6020 J/mol and does not vary appreciably over the temperature range 270-290 K. If 1.40 mol of ice at 0°C is melted by heat supplied from surroundings at 284 K, what is the entropy change in the surroundings in J/K?

A) +30.9
B) -30.9
C) 0.0
D) -27.9
E) +27.9

Question 61

For the process moleene(l) → moleene(g) at 1 atm, ΔH°vap = 26.0 kJ/mol and ΔS°vap = 83.4 J/mol•K. Assuming these values are independent of T, what is the normal boiling point of moleene?

A) 585°C
B) 312°C
C) 39°C
D) -39°C
E) 382°C

Question 62

The dissociation of hydrogen
H₂(g) 2H(g)

A) is spontaneous at high temperature.
B) is spontaneous at low temperature.
C) is independent of temperature.
D) is spontaneous at any temperature.
E) never takes place.

Question 63

The vapor pressure of Br₂(l) at 25°C is 0.281 atm, and 193 J is required to vaporize 1.00 g of bromine at 1 atm pressure.
Calculate ΔS° for the vaporization of Br₂(l) at 25°C and 1 atm.

A) 103 J/K•mol
B) 92.8 J/K•mol
C) 30.8 J/K•mol
D) 0 J/K•mol
E) none of these

Question 64

Consider the reaction
2N₂O₅(g) 4NO₂(g) + O₂(g)
At 25°C, for which the following data are relevant:
Which of the following is true for this reaction?

A) Both ΔH° and ΔS° favor the reaction's spontaneity.
B) ΔH° opposes the reaction, but ΔS° favors it.
C) Both ΔH° and ΔS° oppose the reaction's spontaneity.
D) The reaction cannot occur at room temperature.
E) ΔH° favors the reaction, but ΔS° opposes it.

Question 65

Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423°C). For the process X(l) → X(g) at 1 atm and 423°C, calculate the value of:
Consider the freezing of liquid water at -10°C. For this process what are the signs for ΔH, ΔS, and ΔG, respectively?

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

Question 66

In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C.Calculate ΔH.

A) -59.5 kJ
B) 0 kJ
C) 59.5 kJ
D) -119 kJ
E) none of these

Question 67

Assuming ΔH° and ΔS° are temperature independent, calculate the normal boiling point of bromine.

A) 25°C
B) 332°C
C) 0°C
D) 332 K
E) none of these

Question 68

The vapor pressure of Br₂(l) at 25°C is 0.281 atm, and 193 J is required to vaporize 1.00 g of bromine at 1 atm pressure.
Calculate ΔH° for the vaporization of Br₂(l) at 25°C and 1 atm.

A) 15.4 kJ/mol
B) 0.193 kJ/mol
C) 1.21 kJ/mol
D) 30.8 kJ/mol
E) none of these

Question 69

When a stable diatomic molecule spontaneously forms from its atoms, what are the signs of ΔH°, ΔS°, and ΔG°, respectively?

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

Question 70

In which case must a reaction be spontaneous at all temperatures?

A) ΔS = 0, ΔH is positive
B) ΔH is negative, ΔS is positive
C) ΔH = 0, ΔS is negative
D) ΔH is positive, ΔS is positive
E) none of these

Question 71

For the process involving compound A: A(s) → A(l), ΔH° = 8.8 kJ/mol, and ΔS° = 37.4 J/mol•K. What is the melting point of compound A?

A) 235°C
B) 38°C
C) -38°C
D) -235°C
E) -227°C

Question 72

For a spontaneous endothermic process, which conditions must hold?
1) w_max = ΔG
2) ΔS_surr > 0
3) ΔS cannot be negative.
4) ΔS is positive.

A) all
B) none
C) 1 and 3 only
D) 1, 2, and 4 only
E) 3 and 4 only

Question 73

Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423°C). For the process X(l) → X(g) at 1 atm and 423°C, calculate the value of:
ΔS

A) 0
B) 103 J/K•mol
C) -79.6 J/K•mol
D) 79.6 J/K•mol
E) -103 J/K•mol

Question 74

Calculate ΔG for the vaporization of Br₂(l) at 25°C and 1 atm.

A) 3.15 kJ/mol
B) 0.263 kJ/mol
C) 0
D) 0.378 kJ/mol
E) none of these

Question 75

As O₂(l) is cooled at 1 atm, it freezes at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has a different crystal structure. Thermal measurements show that ΔH for the I → II phase transition is -743.1 J/mol and that ΔS for the same transition is -17.0 J/K mol. At what temperature are Solids I and II in equilibrium?

A) 43.7 K
B) 2.06 K
C) 53.4 K
D) 31.5 K
E) They can never be in equilibrium because they are both solids.

Question 76

Elemental sulfur exists in two crystalline forms, rhombic and monoclinic. From the following data, calculate the temperature at which monoclinic sulfur and rhombic sulfur are in equilibrium.

A) 0 K
B) +450 K
C) +210 K
D) -210 K
E) -450 K

Question 77

For the vaporization of a liquid at a given pressure,

A) ΔG is positive at all temperatures.
B) ΔG is negative at all temperatures.
C) ΔG is positive at low temperatures but negative at high temperatures (and zero at some temperature).
D) ΔG is negative at low temperatures but positive at high temperatures (and zero at some temperature).

Question 78

For the reaction A + B → C + D, ΔH° = +40 kJ and ΔS° = +50 J/K. Therefore, the reaction under standard conditions is

A) spontaneous only at temperatures between 10 K and 800 K.
B) spontaneous at temperatures greater than 800 K.
C) spontaneous at all temperatures.
D) nonspontaneous at all temperatures.
E) spontaneous at temperatures less than 10 K.

Question 79

At constant pressure, the reaction
2NO₂(g) → N₂O₄(g)
Is exothermic. The reaction (as written) is

A) spontaneous at low temperatures but not at high temperatures.
B) spontaneous at high temperatures but not at low temperatures.
C) always spontaneous.
D) never spontaneous.

Question 80

Given the following data, calculate the normal boiling point for formic acid (HCOOH).

A) 115°C
B) 82°C
C) 2.57 K
D) 1730°C
E) 388°C