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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 reaction CaCO3 (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: Edexcel Chemistry (9CH0), A-level, Topic 11: Equilibrium II. Topic: Equilibria.

Key terms in this lesson

colorimetry
A technique that measures the concentration of a coloured solution from how much light of a particular wavelength it absorbs.
titration
A technique for finding the volume of one solution that exactly reacts with a known volume of another, used to find concentration.

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