The reaction, A→B follows first order kinetics. Initial concentration of ‘A’ is 8M. Rate of the reaction after 300 minutes will be (Half life period of the reaction =100 minutes)

For a first order reaction; K=0.693t12=0.693100min-1; Amount left,(a-x)=Initial amounta2n; n=number of half lives; n=300100=3; (a-x)=823=1 M; After 300 minutes, rate=K(a-x)1; rate=0.693100(1) rate=6.93×10-3mol lit-1min-1