Learning Objectives

Reversible Reactions

A reaction is reversible when both the Forward and Reverse reaction can take place under given conditions.

For a reversible reaction to occur, the activation energy of both reactions must be small (so it can occur naturally) and there must be a low enthalpy change (so the activation energies are of a similar size).

When the activation energy for the reverse reaction is not substantially higher than the forward reaction, the reaction will generally be reversible.

Physical processes (such as H₂O (l) ⇌ H₂O (g)) are generally reversible, as energy change is usually low (compared to chemical changes).

In reversible reactions there is a forward and reverse reaction

Forward reactions are from Left to Right (Reactants to Products)

Reverse reactions from Right to Left (Products to Reactants)

Equilibrium

In a reversible reaction, conditions may favour the rate of one reaction.

When the forward reaction occurs at a faster rate than the reverse reaction, the reaction is a “net forward reaction”.

The net forward reaction decreases over time as the rates balance out again.

When there is no net change in rate of reaction or concentration of particles, the reaction is said to be in a “state of equilibrium”, where the foward reaction rate is equal to the reverse reaction rate.

The system is also in equilibrium if the rate of change for concentration of both equations are constant.