Chemical Equilibria

This lesson covers dynamic equilibrium, the equilibrium constants Kc and Kp, le Chatelier's principle, homogeneous and heterogeneous equilibria, ICE tables, and the industrial importance of equilibrium. Understanding equilibrium is essential for predicting the composition of reaction mixtures and optimising industrial processes.

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Dynamic Equilibrium

Key Definition: A dynamic equilibrium is established in a closed system when the rate of the forward reaction equals the rate of the reverse reaction, so that the concentrations of reactants and products remain constant.

At equilibrium:

• The concentrations of reactants and products remain constant (but not necessarily equal).
• Both the forward and reverse reactions continue to occur — the equilibrium is dynamic, not static.
• There is no change in macroscopic properties (colour, pressure, concentration) even though molecules are constantly reacting.

Dynamic equilibrium can only be established in a closed system — one where no substances can enter or leave.

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The Equilibrium Constant Kc

For the general equilibrium: aA + bB ⇌ cC + dD

The equilibrium constant in terms of concentration is:

Kc = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ