Entropy and Free Energy

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

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

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

Entropy (S) = Disorder

Entropy (S) and Phase Changes

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

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

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

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)?

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

Gibb’s Equation

Gibb’s Equation: Predicting Spontaneity