Home Chapter 19 Problem Solving Center Practice Exercises

# 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?Online Text

 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?Online Text

 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?Online Text

 (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.Online Text

 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 Ssys 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 ofS° 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 Kp 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?Online Text

 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?Online Text

 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.Online Text

 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, 7.27 J 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.Online Text

 -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?Online Text

 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 reactionCaCO3(s) --> CaO(s) + CO2(g)Online Text

 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