7.1.1—What is meant by a reversible reaction

A reversible reaction can form products from reactants and also regenerate reactants from products. It is represented with a double arrow when both directions are relevant.

The forward and reverse reactions may have different rates. In a closed system, the composition can settle at a dynamic equilibrium where both continue.

N₂O₄(g) ⇌ 2NO₂(g) allows colourless N₂O₄ to form brown NO₂ and brown NO₂ to recombine. The observed colour depends on the equilibrium composition.

Reversible does not mean the reaction stops or that the amounts become equal. It means both directions occur under the conditions.