1. General Chemistry II CHEM 152 Unit 3 Week 11

2. Week 11 Reading Assignment Chapter 17 – Sections 17.2 (spontaneous), 17.3 (entropy), 17.4 (  S), 17.5 (Gibbs)

3. You Predict – IF left on the stove will sugar burn to make CO 2 and Water? Yes, the Reaction Has a clear Direction.

7. You PREDICT In our classroom what is the chance that all the oxygen in the air will move only to the teacher’s desk and all the nitrogen will move to the students resulting in choking? . . Does Not Happen Non-spontaneous O 2 O 2 O 2 O 2 O 2 O 2 N 2 N 2 N 2 N 2 N 2 N 2 N 2 N 2

8. Product-Favored Reactions One property common to thermodynamically favored processes is that the final state is more DISORDERED or RANDOM than the original Why does a gas tend to expand Into an empty chamber and not The opposite?

9. Will spilled chemicals by themselves jump back into the tank? Systems tend toward Greater disorder Than to organization.

10. Entropy, S The degree of dispersal of matter and energy (ENTROPY) in a system can be quantified experimentally What is the entropy of ice at 0 K?

17. Increases in Entropy

18. What happens to The ENTROPY (S) When a gas dissolves In a liquid?

20. Predicting Entropy Changes,  S For each process, predict whether the entropy of the system increases (  S sys >0 ) or decreases (  S sys <0 )

22. Calculating Entropy Changes,  S

25. Entropy and Temperature S increases slightly with T S increases a large amount with phase changes

29. Studying every known product-favored (spontaneous) reaction we observe 2nd Law of Thermodynamics A reaction is product-favored (spontaneous) if the total entropy of the universe increases ∆ S universe = ∆S system + ∆S surroundings ∆S universe > 0 for product-favored process

30. 2nd Law of Thermodynamics ∆ S universe = ∆S system + ∆S surroundings ∆S universe > 0 0 < ∆S system + ∆S surroundings but ∆S surroundings = ∆ H surroudings /T = - ∆H system /T Because heat into the system is equal but opposite to heat out of the surroundings.

31. 2nd Law of Thermodynamics 0 < ∆S system - ∆H system /T or 0 > ∆H system - T∆S system These are all variables of the system ! They tell us if a process is product favored without measuring the effect on the universe directly!

32. 2nd Law of Thermodynamics ∆ H system - T∆S system < 0 Let’s define ∆ G = ∆H - T∆S If ∆G is negative ( decreases ) - the process is spontaneous (product-favored). This tells us nothing about the speed of the reaction, but that it is product-favored ( spontaneous ).

33. Gibbs Free Energy, G The change of Gibbs free energy is defined as:  G sys =-T  S univ =  H sys - T  S sys The free energy of the Universe decreases in every spontaneous (product-favored) process.  G represents the maximum useful work that can be done by a product-favored system on its surroundings.  G also represents the minimum work that must be done to force a reactant-favored process to occur.

34. Trends with ∆G = ∆H-T ∆S Predict the effect (product-favored or not) on ∆G:

39. Summary Activity Predict the sign of  S for each of the following. Does each process have a tendency to be spontaneous based on entropy change? 2SO 2 (g) + O 2 (g)  2SO 3 (g) Ba(OH) 2 (s)  BaO(s) + H 2 O(g) CO(g) + 2H 2 (g)  CH 3 OH(l) FeCl 2 (s) + H 2 (g)  Fe(s) + 2HCl(g)