The difference between homogeneous and heterogeneous equilibrium lies in the phases of the reactants and products:
- Homogeneous equilibrium:
- All reactants and products are in the same phase (all gases or all liquids).
- Example: In the reaction of nitrogen and hydrogen to form ammonia, all substances are gases.
- Equilibrium constant expression involves all species.
- Heterogeneous equilibrium:
- Reactants and products are in different phases (gas, liquid, or solid).
- Example: Calcium carbonate decomposing into calcium oxide (solid) and carbon dioxide (gas).
- Equilibrium constant expression usually excludes pure solids and liquids, only including gases or aqueous species.
Summary:
- Homogeneous → same phase
- Heterogeneous → different phases
- Only species in gas or aqueous form appear in the equilibrium expression for heterogeneous systems.