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 reaction  Rate of disappearance of H2   =         

rate of reaction

Rate of disappearance of NH3     = rate of reaction

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.

rate of reaction

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 

rate of reaction

The equivalent rate of reaction is,

rate of reaction

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,

rate of reaction

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,

rate of reaction

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

rate of reaction

The rate decomposition of  N2O5        =     rate of reaction

The rate formation of  O2        =          rate of reaction

The rate formation of  NO2     =rate of reaction

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