Entropy and Gibbs Free Energy

1
Entropy and Gibbs Free Energy

• ChemistryMrs. Coyle

2
Spontaneous Process

• A process that occurs without outside
  intervention.
• Spontaneous processes can be fast or slow!

3
What Factors Determine the Spontaneity of a
Reaction?

• Entropy
• Enthalpy
• What ties the two together is
• Gibbs Free Energy.

4
Entropy

• Symbol S
• A measure of molecular randomness or disorder.

5
Disorder

• Chemical processes spontaneously go to a
  direction of increased entropy.
• Why?
• Probability

6
Probability of Disorder

• Is there a higher probability your room will be
  messy or neat as time goes on?

7
System

• the part of the universe under investigation.

8
Entropy of the System

• Is greater in
• Gases than solids.
• Larger volumes of gases than smaller volumes.
• Larger number of gas molecules than smaller
  number of gas molecules.

9
Example

• Which has more entropy in its system?
• H2O (s) or H2O (g)

10
Enthalpy (Heat of Reaction)

• Spontaneity is favored when the process is
  exothermic (DHlt0).

11
Example of a spontaneous exothermic reaction

• 2SO2(g) O2(g)? 2SO3(g) heat
• DHlt0

12
So

• When
• DH lt0 and DSsystemgt0
• (exothermic) (Greater Disorder)
• the reaction would be spontaneous.

13

• Are all spontaneous reactions exothermic and with
  a greater system disorder?
• Answer No.

14
What about exothermic and less disorder? Use
Gibbs Free Energy

• Gibbs Free Energy can be used to predict the
  spontaneity and it ties together the DH and the
  DS, the two driving forces of reactions.
• DG DH-TDS
• (all quantities refer to the system)

15
Gibbs Free Energy

• Energy that can be converted to work.
• DGlt0 for spontaneous processes.
• DG0 at equilibrium.