Law of chemical equilibrium and Kc

Chemical equilibrium can be reached from either side: starting with reactants alone or with products alone leads to the same equilibrium mixture at a given temperature.

Guldberg and Waage's law of mass action: for aA + bB ⇌ cC + dD, Kc = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ at equilibrium, with concentrations in mol L⁻¹.

Kc is constant at a fixed temperature, whatever the starting concentrations.

The equilibrium constant of the reverse reaction is 1/Kc.

Multiplying a balanced equation by n raises K to the power n; dividing by n gives the nth root of K.

Adding two reactions multiplies their equilibrium constants.

Units of Kc are (mol L⁻¹)^Δn; K is dimensionless when Δn = 0, and in thermodynamic treatments K is often taken as dimensionless using standard states.

In calculations, convert equilibrium moles to mol L⁻¹ before substituting; the volume cancels out only when Δn = 0.