Gibbs free energy for equilibria


This section is about using Gibb’s free energy to do calculations involving equilibria, so make sure you’re comfortable with this first!

Gibb’s free energy of A, GA, is:


For the whole reaction, the total change in G is:


In line 3, we assume n = 1. In line 4, we combine the partial pressures using the rules of logs.

At equilibrium ΔG is zero, which gives:


This is a very important equation. It has another form:


Combining this with another equation for Gibb’s free energy:


we get:


and this can be plotted on a graph.

Back to Contents: Chemistry: Equilibria

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