Reversible or Opposing Reactions

In reversible or opposing reactions the products formed also react to give back the reactants.

Initially, the rate of forward reaction is very large which decreases with passage of time and the rate of backward or reverse reaction is zero which increases with passage of item. A stage is reached when two rates become equal. This situation is called the chemical equilibrium. It is dynamic in nature i.e., all the species are reaching at the rate at which they are being formed. A reaction of this type may be represented as

where k_f and k_b are the rate constants of the forward and backward reactions respectively.

The overall rate of reaction is given by

Rate of Reaction = Rate of forward reaction – Rate of backward reaction

Substituting the value of k_b in equation (ii), we get

From this equation we can find the value of k_f from the quantities [A]₀, x_eq and x at time t. All these quantities can be measured easily. From the value of k_f the value of k_b can be calculated by using the relation.