a) How far is his statement true? Give your opinion in this regard. Justify your answer using suitable example.

Question

In a class room discussion about order and molecularity of a chemical reaction, Ramu argued that “there are reactions which appear to be of higher order but actually follow rst order kinetics”. 

a) How far is his statement true? Give your opinion in this regard. Justify your answer using suitable example. 

b) List out any three important dierences between order and molecularity.

Answer 1

a) The reaction appears to be of higher order but actually follows a lower order kinetics. Such reactions are called pseudo order reactions. For example, hydrolysis of ethyl acetate. This reaction appears to be of second order but actually follows rst order kinetics.

CH₃COOC₂H₅ + H₂O⟶H⁺, CH₃COOH + C₂H₅OH

Rate = k [CH₃COOH] [H₂O]

Here the concentration of water does not get altered much during the course of the reaction.

Hence, [H₂O] can be taken as a constant. The equation thus becomes

Rate = k[CH₃COOH] where k = k [H₂O]

Thus, the reaction behaves as a first-order reaction.

(b)

Order	Molecularity
i. Experimental	i. Theorectical
ii. Can be zero	ii. Can not be zero
iii. Can be a fraction	iii. Cannot be a fraction