1. Chemistry 6/e Steven S. Zumdahl and Susan A. Zumdahl Chapter 16: SPONTANEITY, ENTROPY, AND FREE ENERGY Copyright © Houghton Mifflin Company. All Rights Reserved.1

2. 2 Spontaneity, Entropy, and Free Energy Spontaneous Processes and EntropySpontaneous Processes and Entropy React 1 React 2 React 3 React 4 The Effects of Temperature on SpontaneityThe Effects of Temperature on Spontaneity React 5 React 6 React 7 React 8 Entropy Changes in Chemical ReactionsEntropy Changes in Chemical Reactions React 9 React 10 React 11 React 12

3. Copyright © Houghton Mifflin Company. All Rights Reserved.3 Spontaneous Processes and Entropy

4. Copyright © Houghton Mifflin Company. All Rights Reserved.4 Consider 2.4 moles of a gas contained in a 4.0-L bulb at a constant temperature of 32°C. This bulb is connected to an evacuated 20.0-L sealed bulb via a valve. Assume the temperature remains constant. a)What should happen to the gas when you open the valve? b)Calculate  H,  E, q, and w for the process you described above. c)Given your answer to part b, what is the driving force for the process? React 1

5. Copyright © Houghton Mifflin Company. All Rights Reserved.5 Spontaneous Reaction

6. Copyright © Houghton Mifflin Company. All Rights Reserved.6 The Microstates That Give a Particular Arrangement (State) ArrangementMicrostates I II III A B D C A B DC A B D C A B D C A B D C A B D C A B D C A B D C A B D C AB D C A B D C

7. Copyright © Houghton Mifflin Company. All Rights Reserved.7 Predict the sign of  S for each of the following, and explain: a)the evaporation of alcohol b)the freezing of water c)compressing an ideal gas at constant temperature d)heating an ideal gas at constant pressure e)dissolving NaCl in water React 2

8. Copyright © Houghton Mifflin Company. All Rights Reserved.8 For the process A(l)  A(s), which direction involves an increase in energy randomness? Positional randomness? Explain your answer. As temperature increases/decreases (answer for both), which takes precedence? Why? At what temperature is there a balance between energy randomness and positional randomness? React 3

9. Copyright © Houghton Mifflin Company. All Rights Reserved.9 Describe the following as spontaneous/ non- spontaneous/cannot tell, and explain. Provide an example of two of the items below. A reaction that is a)Exothermic and becomes more positionally random b)Exothermic and becomes less positionally random c)Endothermic and becomes more positionally random d)Endothermic and becomes less positionally random e)Explain how temperature affects your answers. React 4

10. Copyright © Houghton Mifflin Company. All Rights Reserved.10 The Effects of Temperature on Spontaneity

11. Copyright © Houghton Mifflin Company. All Rights Reserved.11 Various Possible Combinations of  H and  S for a Process and the Resulting Dependence of Spontaneity on Temperature CaseResult  S positive,   H negative Spontaneous at all temperatures  S positive,   H positive Spontaneous at high temperatures (where exothermicity is relatively unimportant)  S negative,   H negative Spontaneous at low temperatures (where exothermicity is dominant)  S negative,   H positive Process not spontaneous at any temperature

12. Copyright © Houghton Mifflin Company. All Rights Reserved.12 Use the ideas of energy randomness and positional randomness in your discussion of the following: a)Under what conditions is the freezing of water spontaneous? Why? b)Under what conditions is the melting of ice spontaneous? Why? c)Under what conditions is the freezing of water as likely as the melting of ice? Why? React 5

13. Copyright © Houghton Mifflin Company. All Rights Reserved.13 A liquid is vaporized at its boiling point. Predict the signs of w, q,  H,  S,  S surr and  G. Explain your answers. React 6

14. Copyright © Houghton Mifflin Company. All Rights Reserved.14 Now Try These For the process H 2 O(l)  H 2 O(g) at a constant pressure of 1 atm and a constant temperature of 95°C, what is the sign of w? q?  H?  S?  S univ ?  G? Explain. For the process H 2 O(l)  H 2 O(g) at a constant pressure of 1 atm and a constant temperature of 105°C, what is the sign of w? q?  H?  S?  S univ ?  G? Explain.

15. Copyright © Houghton Mifflin Company. All Rights Reserved.15 Now Try These For the process H 2 O(l)  H 2 O(s) at a constant pressure of 1 atm and a constant temperature of 10°C, what is the sign of w? q?  H?  S?  S univ ?  G? Explain. For the process H 2 O(l)  H 2 O(s) at a constant pressure of 1 atm and a constant temperature of -10°C, what is the sign of w? q?  H?  S?  S univ ?  G? Explain.

16. Copyright © Houghton Mifflin Company. All Rights Reserved.16 Rubidium has a heat of vaporization of 69.0 kJ/mol at its boiling point (686°C). For the process Rb(l)  Rb(g) (1 atm, 686°C) Calculate: a)  E (in kJ/mol) b)  S (in J/K mol) c)  G (in kJ/mol) React 7

17. Copyright © Houghton Mifflin Company. All Rights Reserved.17 The value of  H vaporization of substance X is 45.7 kJ/mol, and its normal boiling point is 72.5°C. Calculate  S,  S surr, and  G for the vaporization of one mole of this substance at 72.5°C, 1 atm. React 8

18. Copyright © Houghton Mifflin Company. All Rights Reserved.18 Entropy Changes in Chemical Reactions

19. Copyright © Houghton Mifflin Company. All Rights Reserved.19 Gas A 2 reacts with gas B 2 to form gas AB at constant temperature and pressure. The bond energy of AB is much greater than that of either reactant. What can be said about the sign of:  H?  S surr ?  S?  S univ ? Explain. React 9

20. Copyright © Houghton Mifflin Company. All Rights Reserved.20 A stable diatomic molecule spontaneously forms from its atoms at constant temperature and pressure. Predict the signs of  H°,  S°, and  G°. Explain your answers. React 10

21. Copyright © Houghton Mifflin Company. All Rights Reserved.21 Consider the following system at equilibrium at 25°C. PCl 3 (g) + Cl 2 (g) PCl 5 (g)  G° = -92.50 kJ What will happen to the ratio of partial pressure of PCl 5 to partial pressure of PCl 3 if the temperature is raised? Explain completely. React 11

22. Copyright © Houghton Mifflin Company. All Rights Reserved.22 Sketch a graph of G vs. P H vs. P ln K vs. 1/T (for both endothermic and exothermic cases) React 12