Question

A first order reaction is 50% completed in $1.26\times {10}^{14}s.$ How much time would it take for 100% completion ?

$\left(a\right)1.26\times {10}^{15}s\left(b\right)2.52\times {10}^{14}s\left(c\right)2.52\times {10}^{28}s\left(d\right)Infinite$

Answer 1

The time is taken for half the reaction to complete. i.e., the time in which the concentration of a reactant is reduced to half of its original value is called half-life period of the reaction.

But it is impossible to perform 100% of the reaction. The whole of the substance never reacts because, in every half-life, 50% of the substance reacts. Hence, the time taken for 100% completion of a reaction is infinite.

The reaction would be 100% complete only after infinite time which cannot be calculated.