Entropy and Free Energy

1. Entropy and Free Energy

2. Learning Objectives • Use the Gibbs free-energy equation to determine whether a reaction is spontaneous or not. • Understand the concept of entropy • Be able to identify when entropy increases in a chemical reaction or process

3. Spontaneous Reactions • Spontaneous reactions favor the formation of products • Nonspontaneous reactions do not favor the formation of products, favor reactants • Spontaneity does not indicate speed Example … diamond to graphite • In most reversible reactions, one reaction is spontaneous, the other nonspontaneous

4. Entropy (S) = Disorder The natural tendency of the universe is to become more random. S + 2nd Law of Thermo-dynamics

5. Entropy (S) = Disorder

6. Entropy (S) and Phase Changes

7. Entropy (S): Dividing into Parts-Dissolving Increasing Entropy

8. Entropy (S) Favors More Products Electricity Electrolysis of water Increasing Entropy

9. Entropy (S) Increases with Increasing Temperature Solid Temperature Liquid Increasing Entropy

10. Does a reaction occur? • To determine if a chemical reaction will occur, ask the following questions: 1. What is the change in enthalpy (+H or - H )? 2. What is the orderliness of the products (+S or -S)? (change in entropy) 3. Does it release free energy (-G)?

11. Gibbs Free Energy (G) • G stands for Gibbs free energy It is energy that can do work • -G, the reaction is spontaneous • +G, the reaction is nonspontaneous

12. Gibb’s Equation

13. Gibb’s Equation: Predicting Spontaneity