Let’s consider a reaction

N2 + 3H2 → 2NH3

The rate of reaction can be expressed as,

Rate of disappearance of N_{2} = Rate of disappearance of H_{2} =

Rate of disappearance of NH_{3} =

Here, during disappearance of 1 mole of N, 3 mols of H_{2} are disappeared. So, the rate of disappearance of H_{2} is 3 times the rate of disappearance of N_{2}.

The disappearance of 1 mole of N_{2} gives 2 moles of NH_{3}. So the rate of formation of NH_{3} is 2 times the rate of disappearance

The equivalent rate of reaction is,

Therefore, the equivalent rate of a reaction is obtained by dividing the rate of each species by its stoichiometric coefficient,

aA + bB → cC + dD

The equivalent rate of reaction is,

For the reaction,

H_{2} + I_{2 } → 2HI

The rate of disappearance of H_{2} is 1 × 10^{-6} mol ^{–} litre^{-1} S^{-1}

Calculate the rate of formation of HI

We have,

Express the rate of reaction in terms of all species for decomposition of N_{2}O_{5}. If the rate of formation of O_{2} is 2× 10^{-4} mol lit^{-1} S^{-1} calculate the rate of disappearance of N_{2}O_{5} and rate of formation of N_{2}.

2 N_{2}O_{5} → 4 NO_{2} + O_{2}

The rate decomposition of N_{2}O_{5} =

The rate formation of NO_{2} =