Chemistry › Section P · Thermodynamics › Topic P.4
Gibbs free energy
The second law needs entropy changes for both a system and its surroundings, which is awkward in practice. Gibbs free energy folds both into one property of the system alone, and its change tells you whether a reaction is spontaneous, how temperature affects that, and how far the reaction goes before reaching equilibrium.
In this topic
- One number instead of two
- Defining G and why it works
- Two ways to find ΔG°
- Worked example: ammonia at 25 °C
- Temperature and the four cases
- Worked example: where ammonia synthesis stops being spontaneous
- Free energy, work and coupled reactions
- Free energy and equilibrium
- Worked example: an equilibrium constant from ΔG°
- Common mistakes to avoid
- Key takeaways
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