The relationship between enthalpy (H), entropy (S), and free energy (G) is central in thermodynamics, as it helps predict whether a chemical reaction or process will occur spontaneously.
Key points:
- Enthalpy (H):
- Represents the total heat content of a system.
- Reactions that release heat are exothermic (ΔH < 0), and reactions that absorb heat are endothermic (ΔH > 0).
- Entropy (S):
- Measures the degree of disorder or randomness in a system.
- An increase in disorder corresponds to ΔS > 0; a decrease corresponds to ΔS < 0.
- Gibbs Free Energy (G):
- Combines enthalpy and entropy to determine reaction spontaneity.
- A process is spontaneous if the free energy decreases (ΔG < 0).
- Relationship:
- Free energy change depends on both enthalpy and entropy.
- Even an endothermic reaction (absorbs heat) can be spontaneous if it leads to a significant increase in entropy.
- Conversely, an exothermic reaction may be non-spontaneous if it greatly decreases entropy.
In simple terms:
- Enthalpy tells us energy change.
- Entropy tells us disorder change.
- Free energy tells us if the reaction can happen on its own by combining both energy and disorder effects.