Gibb's free energy

• There are two factors that can affect whether a reaction occurs

  1) Enthalpy

  2) Entropy

• It is possible to use both of these factors together to determine a reaction’s feasibility using Gibb’s free energy

△G = △H - T△S

• △G is the Gibb’s free energy, it is has a negative value then the reaction is feasible

• △G < 0 then reaction is feasible

• △H is the enthalpy change for the reaction in kJmol^-1

• T is the temperature in Kelvin

• △S is the entropy change for the reaction in JK^-1mol^-1

• You must convert entropies into kJK^-1mol^-1 by dividing by 1000

• We can use △G = △H - T△S to determine what temperature a reaction become feasible

• This happens when △G = 0

• Rearrange the equation

  • 0 = △H - T△S

  • △H = T△S

  • △H / △S = T

• Show rearrangement as there are often marks for it

Conditions for feasibility