The relationship between Gibbs free energy (ΔG) and entropy (ΔS) is very important because it helps explain whether a reaction is spontaneous. Here’s a explanation:
1. How they are connected
- Gibbs free energy depends on two things:
- Enthalpy (energy released or absorbed)
- Entropy (disorder or randomness)
- A reaction is more likely to be spontaneous when:
- It releases energy (favorable enthalpy change)
- OR it increases disorder (favorable entropy change)
2. Key points
- Positive entropy change (ΔS > 0) → tends to decrease Gibbs free energy → reaction more likely to be spontaneous.
- Negative entropy change (ΔS < 0) → tends to increase Gibbs free energy → reaction less likely to be spontaneous.
- Temperature matters:
- At higher temperatures, entropy changes become more significant in determining spontaneity.
3. Everyday examples
- Ice melting → entropy increases as solid becomes liquid → ΔG becomes negative → spontaneous above 0°C.
- Water freezing → entropy decreases as liquid becomes solid → ΔG is negative only at low temperatures.
Summary
- Entropy measures disorder, and Gibbs free energy measures spontaneity.
- Reactions that increase disorder (increase entropy) tend to decrease Gibbs free energy and happen naturally.