Chemical Equilibria (AQA A-Level Chemistry): Revision Notes

1.8.1 Chemical Equilibria

Reversible Reactions and Dynamic Equilibrium

Many chemical reactions are reversible, meaning they can proceed in both forwards and reverse directions. A reaction reaches equilibrium when the rates of the forwards and reverse reactions are equal, and the concentrations of the reactants and products remain constant. It's important to note that:

• Forward and reverse reactions occur at the same rate.
• Concentrations of both reactants and products stay constant at equilibrium, though they are not necessarily equal.

Characteristics of Dynamic Equilibrium

In a closed system, where no substances can enter or leave, a dynamic equilibrium occurs. Although the concentrations remain constant, both forwards and reverse reactions continue to happen simultaneously.

For example, in the reaction:

At equilibrium, the rate at which A and B react to form C and D is equal to the rate at which C and D break down to form A and B.