A first order reaction: A `rarr` Products and a second order reaction: 2R `rarr` Products both have half time of 20 min when they are carried out taking 4 mol `L^(-1)` of their respective reactants. The number of mole per litre of A and R remaining unreacted after 60 min from the start of the reaction, respectively, will be

Options

A. 1 and 0.5 M
B. 0.5 M and negligible
C. 0.45 and 1 M
D. 1 and 0.25 M

Answer

C

Explanation

In the case of first order reaction `t_(1//2)` will reamain constant independent of initial concentration so That is after 60 min 0.5 mol `L^(-1)` of a will be left unreacted
In the case of second order reaction `t_(1//2)` is inversely proportional to the intial concentration of reactant `t_(1//2)` a will be constant so `4 mol^(-1) overset(20 min)rarr2 mol L^(-1) overset(40 min)rarr mol l^(-1)` That is after 60 min the concentration of R remaining unreacted will be 1 mol `L^(-1)`