plz explain the concept of pseudo unimolecular reactions......thanks..

Dear student,

Measuring a second order reaction rate with reactants A and B can be problematic: the concentrations of the two reactants must be followed simultaneously, which is more difficult; or measure one of them and calculate the other as a difference, which is less precise. A common solution for that problem is the pseudo first order approximation

If either [A] or [B] remain constant as the reaction proceeds, then the reaction can be considered pseudo first order because in fact it only depends on the concentration of one reactant. If for example [B] remains constant then:

where k' = k[B]₀ (k' or k_obs with units s⁻¹).