Question

Define Half life period of a reaction $\left(t_{1/2}\right)$.

Answer 1

The half life $\left(t_{1/2}\right)$ of a reaction is the time in which the concentration of reactant is reduced to one half of its initial concentration $[R{]}_0$ .
For a first order reaction , $t_{1/2}=\frac{0.693}{k}$ , i.e., independent of $[R{]}_0$.
For a zero order reaction , $t_{1/2}=\frac{[R{]}_0}{2k}$ , i.e., $t_{1/2}\propto [R{]}_0$.