CHEMISTRY COMMUNITY

What is the difference between homogenous and heterogenous equilibria?

A homogenous equation includes substances where all of the phases are the same, for example all gases, and a heterogenous equation has a mixture of different phases.

Another important thing to note is that when a heterogeneous reaction has reactants or products indicated as solids or pure solvents (like H2O), we must write them as "1" when we are writing an expression for K or Q. For instance, in a heterogeneous reaction with an acid HA and H2O as reactants and H3O+ and A- as products, we write K as [H3O+][A-]/[HA]. I didn't include the concentration of water because it is a pure solvent, so leave it in the denominator as 1.

Sam McNeill 1E wrote:A homogenous equation includes substances where all of the phases are the same, for example all gases, and a heterogenous equation has a mixture of different phases.

Here's a couple of examples that I think illustrate this well:
homogeneous: N2 (g) +3 H2 (g) -> 2 NH3 (g)
heterogeneous: CaCO3 (s) -> CaO (s) + CO2 (g)

Heterogenous equations contain compounds with different (hetero) phases while homogenous equations contain the same (homo) phases. For example a chemical equation with all of the compounds in the gas phase is homogenous.

Homogeneous equations are all in the same state of matter, while heterogeneous are in mixed states of matter.

And remember that terms in reactions that are solids or pure liquids are left out of the equilibrium constant.