Entropy and Gibbs Free Energy

Entropy and Gibbs Free Energy ChemistryMrs. Coyle

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

What Factors Determine the Spontaneity of a Reaction? • Entropy • Enthalpy • What ties the two together is: Gibbs Free Energy.

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

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

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

System the part of the universe under investigation.

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.

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

Enthalpy (Heat of Reaction) • Spontaneity is favored when the process is exothermic (DH<0).

Example of a spontaneous exothermic reaction: • 2SO2(g)+ O2(g) 2SO3(g) + heat • DH<0

So…… : • When DH <0 and DSsystem>0 (exothermic) (Greater Disorder) the reaction would be spontaneous.

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

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)

Gibbs Free Energy • Energy that can be converted to work. • DG<0 for spontaneous processes. • DG=0 at equilibrium.

Entropy and Gibbs Free Energy