InterviewSolution
Saved Bookmarks
InterviewSolution
| 1. |
How many half-lives are needed to complete the zeroth order reaction ?A. TwoB. FourC. InfiniteD. Eight |
|
Answer» Correct Answer - A The half-life of a reaction, symbolized by `t_(1//2)` , is the time required for the reactant concentration to drop to one half of its intial value. Suppose a zero order reaction of the from `a0` initial concentration `ArarrB` `(a-x)x` concentration at time `t` Integrated rate law is `K_(0)=(x)/(t)` where `K_(0)` is the rate constantl of a zero order reaction. When `t=t_(1//2)` , half of the reatant is converted into product. thus `x=a//2` . Using integrated rate law, we can write `t_(1//2)=(a)/(2K)` Multiplying both sides by `2` , we get `2t_(1//2)=(a)/(K)=t_(oo)` where `t_(oo)` is the time taken for the completion of the reaction. Thus, two half lives are required to complete the zero order reaction. For first order reaction, the integrated rate law is `t=(2.303)/(k)log((a)/(a-x))` Substituting the value of `K` in terms of half-life we get `t=(2.303)/(0.693//t_(1//2))log((a)/(a-x))` When reaction is complete, `t=t_(oo)` and `x=a` . Therefore `t_(oo)=(2.303t_(1//2))/(0.693)log((a)/(a-a))` `=(2.303)/(0.693)t_(1//2)log((a)/(0))` `=(2.303)/(0.693)t_(1//2)(oo)` Therefore, infinite half lives are needed to complete a first order reaction. |
|