Dr. RogersThermodynamic HomeworkChem 112

1. What is the sign of the entropy change for each of the following processes? The system appears in bold and is underlined. Your answer should be either (+) or (-)

  1. Iodine sublimes
  2. Ethyl alcohol condenses in a flask
  3. Hydrogen andoxygen combine to form water
  4. An artisan makes a pattern from yarn
  5. Wood and oxygen are burned to provide heat
  6. Water evaporates
  7. Molten gold freezes
  8. Butter melts

2. Which of the following reactions will have a S < 0? You must select all of the correct answers.

  1. CaO(s) + H2O(l) Ca(OH)2(s)
  2. NH3(g) + HCl(g) NH4Cl(s)
  3. Br2(g) + 3Cl2(g) 2BrCl3(g)
  4. I2(s) I2(g)

3. Which of the following reactions (equations unbalanced) would be expected to be spontaneous at 25 oC and 1 atm?

A. Al2O3(s) + Fe(s)  Fe2O3(s) + Al(s)

B. PbO(s) + NH3(g) Pb(s) + N2(g) + H2O(g)

C. 2CH4(g) C2H6(g) + H2(g)

4. Which of the following has the largest entropy at 298 K?

A.Xe(g)B.Ne(g)C.Kr(g)D.He(g)E.Ar(g)

5.Which of the following has the largest entropy at 298 K?

A.CH3Cl(g) B. CH3Cl(l)C.CCl4(g)D. CH4(g)E. CCl4(l)

6. Which of the following reactions has the largest positive molar entropy change?

A)PCl5(g) PCl3(g) + Cl2(g)

B)N2(g) + 3H2(g) 2NH3(g)

C)KClO4(s) + 4C(s) KCl(s) + 4CO(g)

D)H2O(s) H2O(g)

E)CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

7.If the enthalpy of fusion of water at its normal melting point is 6.00 kJ/ mol, calculate S° for freezing 1.0 mole of water at this temperature.

8.The enthalpy of vaporization of ethanol, C2H5OH, is 38.7 kJ/ mol at its normal boiling point, 78°C. Calculate S° for vaporization of 1 mole of ethanol at its normal boiling point.

9. For the melting of aluminum, Al(s) Al(l), Ho = 10.0 kJ/ mol and So = 9.50 J/mol· K. Calculate the melting point of Al in Kelvin.

10. The heat of vaporization of mercury is 60.7 KJ/ mol. For Hg(l), S = 76 J/mol K and for Hg(g) S = 175 J/ mol K. Estimate the normal boiling point of liquid mercury.

11. What is the normal boiling point of nitromethane (CH3NO2) in Kelvin.

CH3NO2 (l)CH3NO2 (g)

H = -113.1 kJ/molH = -74.73 kJ/mol

S = 171.76 J/mol KS = 274.42 J/mol K

12. Given the following data, what is the G for this reaction at 298 K and is it spontaneous or nonspontaneous?

2SO2(g) + O2(g)  2SO3(g)

(kJ/ mol–1)–301 –372

13. A reaction is spontaneous at all temperatures if

A.H and S are both positive.

B.H and S are both negative.

C.H is positive and S is negative.

D.H is negative and S is positive.

14. Use the thermodynamic data in appendix D to Calculate G in KJ for the following reaction to determine if it is spontaneous or not.

CO(g) +Cl2(g)  COCl2(g)

COCl2 (g) H = -204.6 kJ/mol

15.Which of the following conditions will result in a spontaneous reaction at all temperatures?

A)H > 0, S < 0

B)H > 0, S = 0

C)H < 0, S < 0

D)H > 0, S > 0

E)H < 0, S > 0

16.Calculate Gr° for the decomposition of ammonium nitrate at 298 K.

NH4NO3(s)→N2O(g)+2H2O(l)

Hf°, kJ/ mol–365.56 82.05–285.83

S°, J/ mol· K 151.08219.85 69.91

17.Calculate Gr° for the decomposition of mercury(II) oxide at 298 K.

2HgO(s)→2Hg(l)+O2(g)

Hf°, kJ/ mol–90.83

S°, J/ mol ·K 70.2976.02205.14

18.For a reaction, Hr° = –92 kJ and Sr° = –65 J/K. Calculate the value of Gr° for this reaction at 25°C.

19.For the following reaction: CuO(s) + H2(g) → Cu(s) + H2O(g)

at 298 K, Hr° = –87.0 kJ and Sr° = 47.0 J/ K. Calculate Gr° at 400 K.

20.For the following reaction: C6H6(g) + 3H2(g) → C6H12(g)

at 298 K, Hr° = –206 kJ and Sr° = –363 J/K. Calculate Gr° at 500°C.

21.For the reaction : 2NH3(g) → 3H2(g) + N2(g)

Hr° = 92.22 kJ and Sr° = 198.75 J/K at 298 K. At what temperatures will this reaction will be spontaneous with all reactants and products in their standard states,

22. What is the sign of the standard free energy change at low temperatures and at high temperatures for the decomposition of phosgene? (Use thermodynamic data in appendix D if necessary)

COCl2(g) → CO(g) + Cl2(g)

23.For the reaction: 2H2(g) + CO(g) → CH3OH(l)

Hr° = –128.13 kJ and Sr° = –332.23 J/K at 298. Calculate Gr° at 100°C.

24. Using thermodynamic values from appendix D calculate G in KJ for the following reaction at 370 K

BaO(s) + CO2(g) → BaCO3(s)

25.Calculate Gr at 298 K for the reaction: C2H5OH(l) → C2H5OH(g, 0.0263 atm)

given Gr° = 6.2 kJ at 298 K.

26. Consider the reaction: NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)

If Kc = 1.75 x 10–5 at 25°C, calculate Gr° for this reaction.

27.Calculate the equilibrium constant at 298 K for the reaction below.

NH3(g) + HCl(g) → NH4Cl(s)

Gf°, kJ/ mol –16.45–95.30–202.87

28.Calculate Gr for the following reaction at 298 K.

Ag(NH3)2+(aq, 0.100 M) → Ag+(aq, 0.00100 M) + 2NH3(aq, 0.00200 M)

Gr° = –41.0 kJ for this reaction at 298 K.

29.If Ksp of AgBr is 7.7 x 10–13 at 298 K, calculate Gr for the reaction of 5 mL of 0.20 M AgNO3(aq) with 5 mL of 0.20 M NaBr(aq) at 298 K.

30.If Gr° = 27.1 kJ at 25°C for the reaction: CH3COOH(aq) + H2O(l) CH3COO–(aq) + H3O+(aq)

calculate Ka for this reaction at 298 K.

31. At 304.8 K, G = -8.686 KJ for the reaction ZnF2(s)Zn2+(aq) + 2F-(aq).

A. Calculate the change in free energy, in KJ at the same temperature when [Zn2+] = 3.5 x 10-2 M and [F-] = 2.3 x 10-3 M. (You may need to use thermodynamic data from appendix D)

B. Is the forward or reverse reaction spontaneous?

32. State how increasing the temperature influences the value of the equilibrium constant for each of the following reactions.

A. N2O4(g) 2NO2(g)

B. 2 CO(g) + O2(g) 2CO2(g)

C. 2HI(g) H2(g) + I2(g)

D. C(s) + H2O(g) CO(g) + H2(g)

33. Consider the phase diagram of a pure compound. Which statement applies?

A.The path AC represents sublimation.

B.Following the path ABC the compound would first liquefy and then

vaporize.

C.If the compound is in state A, continued reduction of the pressure (at constant

temperature) will cause it to melt.

D.None of these statements is correct.

34. In a phase diagram what does the triple point represent?

35. In the phase diagram, which transition represents the condensation of a gas to a liquid?

(A)B to A(B)D to B(C)C to D(D)A to D

Answers:

1. A (+) B (-) C (-) D (-) E (+) F (+) G (-) H (+)2. A B C

3. B4. A5. C

6. C7. –22.0 J/ K8. 110 J/K

9. 1050 K10. 614 K11. 373 K

12. –142 kJ; spontaneous13. D14. -67.43 KJ; spontaneous

15. E16. –186.21 kJ17. +117.1 kJ

18. –73 kJ19. –106 kJ20. +74.6 kJ

21. at temperatures above 464 K.22. high temp G = (-); low temp G = (+)

23. –4.21 kJ 24. -205.6 KJ25. –2.8 kJ

26. 27.1 kJ27. 9.39 x 1015

28. –83.2 kJ29. 57.7 kJ30. 1.78 x 10–5

31. A. -47.9 KJ B. forward32. A. Increase; B Decrease; C increase; D increase

33. D34. the pressure and temperature at which all three phases of a substance can co-exist 35. B