Deck 10: Spontaneity, Entropy, and Free Energy

Question 1

$\Delta$ S_surr is

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

Answer 1

less than zero.

Question 2

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

Answer 2

to the left

Question 3

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 $\Delta$ V.

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

Answer 3

-5.87 L

Question 4

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 5

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

-Calculate $\Delta$ H.

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

Question 6

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 $\Delta$ S slows down the reaction.

Question 7

$\Delta$ G is

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

Question 8

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

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 11

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 $\Delta$ T.

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

Question 12

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. $\Delta$ S

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 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 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 15

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 16

$\Delta$ H is

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

Question 17

Consider the dissociation reaction of the acid HF. Why is $\Delta$ S negative?

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

Question 18

$\Delta$ S is

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

Question 19

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 20

$\Delta$ E is

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

Question 21

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 $\Delta$ E.

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

Question 22

At 1 atm, a liquid is heated above its normal boiling point.

- $\Delta$ S_surr for this process is

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

Question 23

$\Delta$ S_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 24

1.6 mol of an ideal gas at 303 K is compressed isothermally and reversibly from 1.8 L to 0.30 L. What is $\Delta$ S?

A) -7.2 kJ/K
B) 24 J/K
C) -24 J/K
D) -12 J/K
E) -15 J/K

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

At 1 atm, a liquid is heated above its normal boiling point.

- $\Delta$ S_univ for this process is

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

Question 27

$\Delta$ S is _______ for exothermic reactions and ______ for endothermic reactions.

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

Question 28

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 29

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 30

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 $\Delta$ E.

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

Question 31

Calculate $\Delta$ G for the isothermal compression of 1 mol of an ideal monatomic gas from 1.4 atm to 5.6 atm at 24°C.

A) 1.6*10³ J
B) 3.4 *10³ J
C) 5.1*10³ J
D) -3.4* 10³ J
E) -1.6 * 10³ J

Question 32

Which of the following is true?

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

Question 33

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) ( $\Delta$ S_gas = 0)
B) ( $\Delta$ S_gas = Rln2/298)
C) ( $\Delta$ S_surr = 0)
D) ( $\Delta$ S_univ = 0)
E) ( $\Delta$ S_gas = $\Delta$ S_surr)

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 w.

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

Question 35

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 36

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

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

Question 37

If the change in entropy of the surroundings for a process at 446 K and constant pressure is -322 J/K, what is the heat flow absorbed by the system?

A) 144 kJ
B) 722 kJ
C) -144 kJ
D) -17.3 kJ
E) 17.3 kJ

Question 38

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 39

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) ( $\Delta$ S_gas = $\Delta$ S_surr)
B) ( $\Delta$ S_gas = Rln2)
C) ( $\Delta$ S_gas = 0)
D) ( $\Delta$ S_univ = 0)
E) ( $\Delta$ S_surr = 0)

Question 40

At 1 atm, a liquid is heated above its normal boiling point.

- $\Delta$ S for this process is

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

Question 41

When a gas is expanded isothermally and reversibly at 37°C, the work done is -37.8 kJ. Calculate $\Delta$ S.

A) 1.02 kJ/K
B) -1022 J/K
C) -1014 J/K
D) -1.02 kJ/K
E) 1.22 * 10² J/K

Question 42

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) ( $\Delta$ H < 0)
B) ( $\Delta$ S_sys< 0)
C) ( $\Delta$ S_univ > 0)
D) ( $\Delta$ S_surr > 0)
E) none of these

Question 43

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

- $\Delta$ S_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 44

Calculate $\Delta$ S 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 45

The process H₂O(g) $\rightarrow$ 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 46

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

- $\Delta$ G

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 47

4.00 mol of a monatomic ideal gas is cooled from 245°C to 27°C at constant volume. Calculate $\Delta$ S.

A) -19.7 J/K
B) -27.2 J/K
C) -1.10 * 10² J/K
D) -11.8 J/K
E) -45.4 J/K

Question 48

Choose the correct statement.

A) A reaction that exhibits a negative value of $\Delta$ S 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 49

For which process is $\Delta$ S 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 50

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 1.20 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) +26.5
B) -26.5
C) 0.0
D) -23.5
E) +23.5

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 $\Delta$ G.

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

Question 52

Calculate $\Delta$ S for cooling 1.9 mol of an ideal monatomic gas from 89°C to 38°C at constant pressure.

A) -33.6 J/K
B) -3.60 J/K
C) -6.00 J/K
D) -3.16 J/K
E) -2.40 J/K

Question 53

The process H₂O(g) $\rightarrow$ H₂O(l) takes place at 1 atm and 95°C.

-What is $\Delta$ G?

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

Question 54

Calculate $\Delta$ S for cooling 2.84 mol of an ideal monatomic gas from 92°C to 42°C at constant volume.

A) -1.84 J/K
B) -18.5 J/K
C) -3.48 J/K
D) -5.22 J/K
E) -27.8 J/K

Question 55

The process H₂O(g) $\rightarrow$ 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 56

The process H₂O(g) $\rightarrow$ H₂O(l) takes place at 1 atm and 95°C.

-What is $\Delta$ H?

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

Question 57

Calculate the minimum work required to compress 2.9 mol of an ideal monatomic gas from 48.4 L to 17.0 L at 22°C.

A) 11.2* 10³ J
B) 5.5* 10² J
C) 7.4 * 10³ J
D) -11.2*10³ J
E) 2.6 *10² J

Question 58

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

- $\Delta$ S_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 59

The process H₂O(g) $\rightarrow$ H₂O(l) takes place at 1 atm and 95°C.

-What is $\Delta$ S?

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

Question 60

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 $\Delta$ S.

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 61

Calculate $\Delta$ G 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 62

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

A) ( $\Delta$ S = 0, $\Delta$ H is positive)
B) ( $\Delta$ H is negative, $\Delta$ S is positive)
C) ( $\Delta$ H = 0, $\Delta$ S is negative)
D) ( $\Delta$ H is positive, $\Delta$ S is positive)
E) none of these

Question 63

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

- $\Delta$ S

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 64

For a spontaneous endothermic process, which conditions must hold? 1) w_max = $\Delta$ G
2) $\Delta$ S_surr > 0
3) $\Delta$ S cannot be negative.
4) $\Delta$ S is positive.

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

Question 65

When a stable diatomic molecule spontaneously forms from its atoms, what are the signs of $\Delta$ H°, $\Delta$ S°, and $\Delta$ G°, respectively?

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

Question 66

For the reaction A + B $\rightarrow$ C + D, $\Delta$ H° = +40 kJ and $\Delta$ S° = +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 67

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 $\Delta$ H for the I $\rightarrow$ II phase transition is -743.1 J/mol and that $\Delta$ S 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 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 $\Delta$ S° 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 69

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 $\Delta$ H.

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

Question 70

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 71

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 72

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 $\Delta$ H° 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 73

For the vaporization of a liquid at a given pressure,

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

Question 74

Consider the reaction
At 25°C, for which the following data are relevant: Which of the following is true for this reaction?

A) Both $\Delta$ H° and $\Delta$ S° favor the reaction's spontaneity.
B) ( $\Delta$ H° opposes the reaction, but $\Delta$ S° favors it.)
C) Both $\Delta$ H° and $\Delta$ S° oppose the reaction's spontaneity.
D) The reaction cannot occur at room temperature.
E) ( $\Delta$ H° favors the reaction, but $\Delta$ S° opposes it.)

Question 75

For the process moleene(l) $\rightarrow$ moleene(g) at 1 atm, $\Delta$ H $\degree$ vap = 30.0 kJ/mol and $\Delta$ S $\degree$ vap = 78.4 J/mol•K. Assuming these values are independent of T, what is the normal boiling point of moleene?

A) 656°C
B) 383°C
C) 110°C
D) -110°C
E) 381°C

Question 76

For the process involving compound A: A(s) $\rightarrow$ A(l), $\Delta$ H° = 8.8 kJ/mol, and $\Delta$ S° = 36.4 J/mol•K. What is the melting point of compound A?

A) 242°C
B) 31°C
C) -31°C
D) -242°C
E) -228°C

Question 77

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

Question 78

Assuming $\Delta$ H° and $\Delta$ S° 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 79

At constant pressure, the reaction 2NO₂(g) $\rightarrow$ 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

Consider the freezing of liquid water at -10°C. For this process what are the signs for $\Delta$ H, $\Delta$ S, and $\Delta$ G, respectively?

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