Gibbs Free Energy

At any given temperature, enthalpy and entropy are important in determining if a reaction is spontaneous (actually happens). at equilibrium (the forward and reverse reactions occur at the same rate), or non-spontaneous (does not happen...actually the reverse reaction occurs instead at that temperature).

This is because of a quantity called Gibbs Free Energy (ΔG). ΔG must be a negative value for a reaction to be spontaneous.

Temperature must be reported in Kelvin for this to work. Therefore, T cannot be a negative value, as 0 Kelvin is absolute zero (-273°C). That makes making predictions a little easier...

We need to be able to categorise reactions as being one of these:

1. Enthalpy driven, or
2. Entropy driven

We use the equation for Gibbs Free Energy to make this prediction: