# Rate of reaction and stoichiometric coefficient

Let’s consider a reaction

N2 + 3H2      →         2NH3

The rate of reaction can be expressed as,

Rate of disappearance of N2   =           Rate of disappearance of H2   =

Rate of disappearance of NH3     =

Here, during disappearance of 1 mole of N, 3 mols of H2 are disappeared. So, the rate of disappearance of H2 is 3 times the rate of disappearance of N2.

The disappearance of 1 mole of N2 gives 2 moles of NH3. So the rate of formation of NH3 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,

H2 + I2            →             2HI

The rate of disappearance of H2 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 N2O5. If the rate of formation of O2 is 2× 10-4 mol lit-1 S-1 calculate the rate of disappearance of N2O5 and rate of formation of N2.

2 N2O5                       4 NO2 + O2

The rate decomposition of  N2O5        =

The rate formation of  O2        =

The rate formation of  NO2     =