Gibbs free energy for equilibria

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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:

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

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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:

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

scan20012

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

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we get:

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and this can be plotted on a graph.

Back to Contents: Chemistry: Equilibria

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