Write a condition under which a bimolecular reaction is kinetically first order. Give an example of such a reaction

Asked by sanjeet.kumar | 12th Mar, 2019, 02:20: PM

Expert Answer:

When one of the reactants is taken in excess so that its concentration hardly changes.

In such condition, the bimolecular reaction will be of first order.

Example:

Hydrolysis of ethyl acetate (0.01 mol) with 10 mol of water:

space space space space space space space space space space space space space space space CH subscript 3 COOC subscript 2 straight H subscript 5 space space plus space space space space straight H subscript 2 straight O space space space space space rightwards arrow space space space CH subscript 3 COOH space space space plus space space straight C subscript 2 straight H subscript 5 OH
at space straight t space equals space 0 space space space space space space space 0.01 space mol space space space space space space space space space space space 10 space mol space space space space space space space space space space space 0 space mol space space space space space space space space space space space space 0 space mol
at space straight t space equals straight t space space space space space space space space space space 0 space mol space space space space space space space space space space space space space space space space 9.9 space mol space space space space space space space space space 0.01 space mol space space space space space space 0.01 space mol

Here space the space concentration space of space water space does space not space changes space much comma
So space the space rate space of space the space reaction space is comma

Rate space equals space straight k left square bracket CH subscript 3 COOC subscript 2 straight H subscript 5 right square bracket to the power of 1 left square bracket straight H subscript 2 straight O right square bracket to the power of 0

left square bracket straight H subscript 2 straight O space right square bracket space equals constant

therefore space Rate space equals space space straight k left square bracket CH subscript 3 COOC subscript 2 straight H subscript 5 right square bracket to the power of 1

So in this reaction, the concentration of water is taken in excess and the bimolecular reaction behaves as first order reaction.

Answered by Varsha | 12th Mar, 2019, 07:53: PM