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Homogenous and Heterogenous Equilibria and Kc

In homogenous equilibria, all species have the same physical state.N2O4(g) ⇌ 2 NO2(g)In heterogenous equilibria there is a mixture of different physical states.When water is a reactant or product, it appears in the expression for the equilibrium constant.When water is a solvent, it does not appear in the expression for the equilibrium constant. This is because the concentration of water stays constant.Solids are not included in the equilibrium expression.For the reactionCaCO3 (s) ⇌ CaO(s) + CO2(g)Kc =[ CO2(g)]Units of Kc depend on the equilibrium expression e.g.2CHClF2(g) ⇌ C2F4(g) + 2HCl(g)units are moldm-3

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Specification: OCR Chemistry A (H432), A-level, 5.1.2 How far?. Topic: Equilibria.

Key terms in this lesson

equilibrium constant Kc
The value, at a given temperature, of the equilibrium expression written in terms of the concentrations of reactants and products.

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