Practice Exercises

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Chapter 19

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Practice Exercises

This activity contains 32 questions.

Which of the following processes are spontaneous and which are nonspontaneous: (i) separation of N₂ and O₂ molecules in air from each other, (ii) the reaction of sodium metal with chlorine gas to form sodium chloride, (iii) the dissolution of HCl(g) in water to form concentrated hydrochloric acid?

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	(i) spontaneous, (ii) spontaneous, (iii) spontaneous
	(i) spontaneous, (ii) spontaneous, (iii) nonspontaneous
	(i) spontaneous, (ii) nonspontaneous, (iii) spontaneous
	(i) nonspontaneous, (ii) spontaneous, (iii) spontaneous
	(i) nonspontaneous, (ii) nonspontaneous, (iii) spontaneous

The normal boiling point of ethanol is 78.5°C. Is the vaporization of ethanol an endothermic or exothermic process? In what temperature range is the vaporization of ethanol a spontaneous process?
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	endothermic, T < 78.5°C
	exothermic, T < 78.5°C
	endothermic, T > 78.5°C
	exothermic, T > 78.5°C

Consider the thermodynamic quantities E, q, and w. Which of these quantities are state functions?
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	E only
	q only
	w only
	E and q only
	E and w only
	all

How does the entropy of the system change when each of the following occurs (i) a solid is melted, (ii) a liquid vaporizes, (iii) a gas liquefies?
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	(i) increases, (ii) increases, (iii) increases
	(i) decreases, (ii) increases, (iii) increases
	(i) increases, (ii) decreases, (iii) increases
	(i) increases, (ii) increases, (iii) decreases
	(i) decreases, (ii) decreases, (iii) decreases

Mercury freezes at -38.9°C, and its enthalpy of fusion is 2.33 kJ/mol. Calculate the value of

S for the freezing of 1.00 mol of Hg(l) at -38.9°C.

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	-9.95 x 10^-3 J K^-1
	5.99 x 10^-2 J K^-1
	-2.33 J K^-1
	-9.95 J K^-1
	59.9 J K^-1

Calculate the entropy change when 1.50 mol of an ideal gas expands at a constant temperature from an initial volume of 20.0 L to a final volume of 90.0 L.
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	0.185 J K^-1
	8.15 J K^-1
	12.5 J K^-1
	-18.8 J K^-1
	18.8 J K^-1

For each of the following pairs, choose the substance with the higher entropy per mole at a given temperature:

(i) O₂(g) at 5 atm or O₂(g) at 0.5 atm, (ii) Br₂(l) or Br₂(g)

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	(i) O₂(g) at 5 atm, (ii) Br₂(l)
	(i) O₂(g) at 0.5 atm, (ii) Br₂(l)
	(i) O₂(g) at 5 atm, (ii) Br₂(g)
	(i) O₂(g) at 0.5 atm, (ii) Br₂(g)

For each of the following processes, predict whether

S_sys is positive or negative: (i) 2K(s) + Br₂(l) --> 2KBr(s), (ii) 2MnO₂(s) --> 2MnO(s) + O₂(g)

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	(i) positive, (ii) positive
	(i) negative, (ii) positive
	(i) positive, (ii) negative
	(i) negative, (ii) negative

Using the tabulated values of S° in Appendix C, calculate the value of

S° for the reaction

C₂H₄(g) + H₂(g) C₂H₆(g)

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	-120.5 J K^-1
	120.5 J K^-1
	10.1 J K^-1
	-10.1 J K^-1

Using the tabulated values of S° in Appendix C, calculate the value of

S° for the reaction

2CH₃OH(g) + 3O₂(g) 2CO₂(g) + 4H₂O(g)

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	-377.4 J K^-1
	-161.8 J K^-1
	-40.2 J K^-1
	92.3 J K^-1
	313.9 J K^-1

Using data from Appendix C, calculate

G° at 298.15 K for the following process:

H₂(g) + Cl₂(g) 2HCl(g)

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	190.54 kJ
	-262.4 kJ
	262.4 kJ
	-95.27 kJ
	-190.54 kJ

Using data from Appendix C, calculate

G° for the following process:

2NOCl(g) 2NO(g) + Cl₂(g)

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	-40.8 kJ
	-20.4 kJ
	20.4 kJ
	40.8 kJ

For a certain reaction,

H = 45 kJ and

S = 125 J/K. Assume that

H and

S do not vary with temperature. At what temperature will the reaction have

G = 0?

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	0.36 °C
	0.36 K
	360 °C
	360 K
	you cannot solve the problem without additional information

Methanol, CH₃OH, can be made by the reaction of CO with H₂:

CO(g) + 2H₂(g) CH₃OH(g)

H° = -90.7 kJ/mol and S° = -90.88 J mol^-1 K^-1 for this reaction. How is G° for the reaction expected to vary with increasing temperature? Under standard conditions is the reaction spontaneous at 298 K? Explain.

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	G° will increase; the reaction is spontaneous, since G° < 0 at 298 K
	G° will decrease; the reaction is spontaneous, since G° < 0 at 298 K
	G° will increase; the reaction is not spontaneous, since G° < 0 at 298 K
	G° will decrease; the reaction is not spontaneous, since G° > 0 at 298 K
	G° will increase; the reaction is not spontaneous, since G° > 0 at 298 K

Explain qualitatively how

G and Q change for the following reaction as the partial pressure of N₂ is increased.

N₂(g) + 3F₂(g) 2NF₃(g)

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	G will increase, and Q will increase
	G will decrease, and Q will increase
	G will increase, and Q will decrease
	G will decrease, and Q will decrease

Use data from Appendix C to calculate K_p at 298 K for the reaction

H₂(g) + I₂(g) 2HI(g)

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	1.15 x 10^-3
	1.0068
	0.350
	8.70 x 10²
	1.47 x 10³

Which of the following processes are spontaneous?

(i) separation of CO₂ from air to make dry ice

(ii) the reaction of hydrogen with oxygen to form water

(iii) making a sugar solution by dissolving sugar in water

(iv) filling a tire with air at high pressure

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	all
	i
	ii
	iii
	i and iv
	ii and iii

Ice liquefies at 0°C. Is liquefication exothermic or endothermic? In what temperature range is the process spontaneous?
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	endothermic, T > 100°C
	endothermic, 0°C < T < 100°C
	exothermic, T > 100°C
	exothermic, 0°C < T < 100°C
	endothermic, never

Which one of the following processes is irreversible?
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	water heated to 110°C at 1 atm pressure, beginning to boil
	water converting to ice at 0°C
	zinc sulfide solid dissociating to ions in a saturated aqueous solution
	air in a tire with the valve open and with no air escaping
	acetic acid ionizing after being in water for a long time

In which of the following cases does the entropy increase?

(i) gas escaping from a filled tire

(ii) solid melting

(iii) salt precipitating from solution

(iv) calcium carbonate decomposing to form carbon dioxide and calcium oxide

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	all
	i
	ii
	iii
	i, and iv
	i, ii, and iv

The heat of vaporization of diethyl ether is 26.0 kJ/mol at 34.51°C while the heat of fusion is 7.27 kJ/mol at -116.3°C. Calculate the entropies of vaporization and fusion.
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	753 J mol^-1K^-1, 62.5 J mol^-1K^-1
	84.5 J mol^-1K^-1, -46.4 J mol^-1K^-1
	0.0845 J mol^-1K^-1, -0.0465 J mol^-1K^-1
	26.0 J mol^-1K^-1, 7.27J mol^-1K^-1

Calculate the entropy change when a gas with a volume of 30.0 L is compressed to fill a tire with a volume of 10.0 L at constant temperature. Assume there are 1.20 mol of gas and that the gas is ideal.
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	-4.76 J K^-1
	11.0 J K^-1
	-11.0 J K^-1
	-0.108 J K^-1
	-9.13 J K^-1

In which case does the entropy of the system decrease significantly?
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	H₂O(l) --> H₂O(g)
	C(s) + O₂(g) --> CO₂(g)
	SnO₂(s) + 4C(s) --> Sn(s) + 4CO₂(g)
	N₂(g) + 3 H₂(g) --> 2NH₃(g)
	CaCO₃(s) --> CaO(s) + CO₂(g)

In which case(s) below is the entropy of the first substance greater than the entropy of the second?

(i) 1 mol of H₂(g) vs 0.5 mol of H₂(g) at 400 K

(ii) 1 mol of CH₄(g) vs 1 mol of HCl(g) at 300 K

(iii) 1 mol of CaCO₃(s) vs 1 mol of F₂(g) at 300 K

(iv) 1 mol of CH₄(g) at 200 K vs 1 mol of CH₄(g) at 400 K

(v) 1 mol of H₂O(l) at 300 K vs 1 mol of H₂O(g) at 300 K

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	i
	ii
	iii
	iv
	v
	i and ii

Using the tabulated values of S° in Appendix C, calculate the value of

S° for the reaction

CaCO₃(s) --> CaO(s) + CO₂(g)

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	-160.5 J K^-1
	346.2 J K^-1
	160.5 J K^-1
	213.6 J K^-1

Using the tabulated values of S° in Appendix C, calculate the value of

S° for the reaction

2H₂(g) + O₂(g) --> 2H₂O(g)

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	-146.8 J K^-1
	-88.5 J K^-1
	843.8 J K^-1
	524.4 J K^-1
	88.5 J K^-1
	-326.3 J K^-1

Using data from Appendix C, calculate

G° for the reaction

Fe₂O₃(s) + 3C(s, graphite) --> 2Fe(s) + 3CO(g)

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	603.8 kJ
	-1152.6 kJ
	329.4 kJ
	-411.6 kJ

Using data from Appendix C, calculate

G° for the reaction

2NO₂(g) --> N₂O₄(g)

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	-5.40 kJ
	-46.4 kJ
	202.0 kJ
	5.40 kJ

An endothermic reaction has

H = 60 kJ and an entropy change of -120 J/K. Assuming that

H and

S do not vary with temperature, at what temperature will the system be at equilibrium?

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	0.50 K
	never
	500 K
	additional information is needed to solve this problem
	500°C

If a reaction is not spontaneous at room temperature but becomes spontaneous as the temperature is increased (as, for example, the dissociation of calcium carbonate to carbon dioxide and calcium oxide), what can you say about the signs of the enthalpy and entropy changes?

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	H° > 0, S° > 0
	H° < 0, S° < 0
	H° < 0, S° > 0
	H° >0, S° < 0
	H° < 0, S° = 0

Calculate the equilibrium constant at 298 K for the reaction
CaCO₃(s) --> CaO(s) + CO₂(g)
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	130.2
	4.85 x 10^-3
	1.054
	-52.55
	1.5 x 10^-23

In the synthesis of ammonia,

N₂(g) + 3H₂(g) --> 2NH₃(g),

what happens to G and Q if the partial pressure of NH₃ is increased?

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	G will increase and Q will decrease
	G will decrease and Q will decrease
	G will increase and Q will increase
	G will decrease and Q will increase

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Practice Exercises

The normal boiling point of ethanol is 78.5°C. Is the vaporization of ethanol an endothermic or exothermic process? In what temperature range is the vaporization of ethanol a spontaneous process?Online Text

Consider the thermodynamic quantities E, q, and w. Which of these quantities are state functions?Online Text

How does the entropy of the system change when each of the following occurs (i) a solid is melted, (ii) a liquid vaporizes, (iii) a gas liquefies?Online Text

Calculate the entropy change when 1.50 mol of an ideal gas expands at a constant temperature from an initial volume of 20.0 L to a final volume of 90.0 L.Online Text

Ice liquefies at 0°C. Is liquefication exothermic or endothermic? In what temperature range is the process spontaneous?Online Text

Which one of the following processes is irreversible?Online Text

The heat of vaporization of diethyl ether is 26.0 kJ/mol at 34.51°C while the heat of fusion is 7.27 kJ/mol at -116.3°C. Calculate the entropies of vaporization and fusion.Online Text

Calculate the entropy change when a gas with a volume of 30.0 L is compressed to fill a tire with a volume of 10.0 L at constant temperature. Assume there are 1.20 mol of gas and that the gas is ideal.Online Text

In which case does the entropy of the system decrease significantly?Online Text

Calculate the equilibrium constant at 298 K for the reactionCaCO3(s) --> CaO(s) + CO2(g)Online Text

The normal boiling point of ethanol is 78.5°C. Is the vaporization of ethanol an endothermic or exothermic process? In what temperature range is the vaporization of ethanol a spontaneous process?
Online Text

Consider the thermodynamic quantities E, q, and w. Which of these quantities are state functions?
Online Text

How does the entropy of the system change when each of the following occurs (i) a solid is melted, (ii) a liquid vaporizes, (iii) a gas liquefies?
Online Text

Calculate the entropy change when 1.50 mol of an ideal gas expands at a constant temperature from an initial volume of 20.0 L to a final volume of 90.0 L.
Online Text

Ice liquefies at 0°C. Is liquefication exothermic or endothermic? In what temperature range is the process spontaneous?
Online Text

Which one of the following processes is irreversible?
Online Text

The heat of vaporization of diethyl ether is 26.0 kJ/mol at 34.51°C while the heat of fusion is 7.27 kJ/mol at -116.3°C. Calculate the entropies of vaporization and fusion.
Online Text

Calculate the entropy change when a gas with a volume of 30.0 L is compressed to fill a tire with a volume of 10.0 L at constant temperature. Assume there are 1.20 mol of gas and that the gas is ideal.
Online Text

In which case does the entropy of the system decrease significantly?
Online Text

Calculate the equilibrium constant at 298 K for the reaction
CaCO₃(s) --> CaO(s) + CO₂(g)
Online Text