1. Thermodynamics REACTION SPONTANEITY “stuff happens” PART II

2. What are the two things that “all things in the universe want?”

3. All things want: 1. 2.

4. 1. A change in energy that results in a lower energy state is part of a reaction that is EXOTHERMIC ENDOTHERMIC and contributes to helping the reaction be SPONTANEOUS NON-SPONTANEOUS ΔH is POSITIVE NEGATIVE ________________________________________ 2. An increase in entropy contributes to helping the reaction be SPONTANEOUS NON-SPONTANEOUS ΔS is POSITIVE NEGATIVE

5. Sometime, a process is spontaneous in terms of one factor, and non-spontaneous in terms of the other factor. How can you predict if a process will be spontaneous or non-spontaneous?

6. Calculate This is the (assuming constant temperature and pressure) It’s symbol is:

7. For a system: ΔG = The temperature must be in

8. If ΔG is NEGATIVE, the process is SPONTANEOUS NONSPONTANEOUS If ΔG is POSITIVE, the process is SPONTANEOUS NONSPONTANEOUS

9. The more negative the ΔG, the more

10. The more positive the ΔG, the more

11. Since ΔH and ΔS can be either positive (+) or negative (-), there are four possible combinations of ΔH and ΔS. You can predict/calculate whether ΔG will be positive (+) or negative (-), for each combination, and therefore whether a reaction will be spontaneous or non-spontaneous

12. -ΔH+ΔH +ΔS -ΔS HOW ΔH AND ΔS AFFECT ΔG

13. For example, consider fireworks…

14. One of the reactions in the firework we will make is this: NH 4 NO 3 (s) N 2 O(g) + 2H 2 O(g ) Choose one ΔH is POSITIVE NEGATIVE Choose one ΔS is POSITIVE NEGATIVE

15. Next, let’s go back to liquid water and ice. If an ice cube is melting: ΔH is POSTIVE NEGATIVE ΔS is POSITIVE NEGATIVE If liquid water is freezing: ΔH is POSTIVE NEGATIVE ΔS is POSITIVE NEGATIVE What determines which of these reactions will happen – i.e., which is spontaneous?

16. Whether ice melts or liquid water freezes is determined by the ΔG = ΔH - TΔS

17. Finally, Let’s look at one of the single most important reactions for all living things.

18. 2880 kJ + 6CO 2 (g) + 6H 2 O(l) C 6 H 12 O 6 (s) + 6O 2 (g) Is ΔH POSITIVE or NEGATIVE?

19. Looking at the structures of the reactants and products, ** can you tell which has more order? ** is ΔS positive or negative?

20. With a ____ΔH and a ____ ΔS, photosynthesis can ______________ be spontaneous.

21. Human beings are complex, highly organized, and well- ordered systems. Many of the biochemical reactions necessary for us to live and grow are NONSPONTANEOUS

22. These non-spontaneous reactions are made to occur by them with spontaneous reactions.

23. To give you an idea of what this means: A factory produces 2 items – A and B. They make money on A, and lose money on B. They make enough extra money on A to compensate for what they lose on B.

24. To finish: let’s apply the Laws of Thermodynamics to an everyday situation….

25. When you buy gasoline for your car, you are buying

26. One gallon of gasoline contains ~ Calories – about the same as 110 hamburgers. = 110

27. You are paying for 31,000 Calories, but is this what you are getting?

28. The First law of Thermodynamics says:

29. What this means: The First Law says that When you burn that gallon of gasoline, you can’t possibly get than the 31,000 Calories it contains. (But wait…there’s more!)

30. The Second Law Of Thermodynamics says:

31. What this means: The Second Law says: in any spontaneous reaction (like burning gasoline) the entropy of the universe must ___________________ Your gallon of gasoline has 31,000 Calories stored in it; however, when the gas is burned in your car,

32. It’s like you bought a hamburger, but were only allowed to eat

33. So – if you can’t win, and you can’t even break even – why would you “play the game?”

34. Because:

35. Why not?

36. So, the Laws of Thermodynamics say: You can’t win, You can’t even break even, And you can’t get out of the game! With this final thought, I bid you – Have a good summer!