Question

For a reaction, the half-life is independent of initial concentration. What is the order of that reaction?

• A. Zero
• B. One
• C. Two
• D. Three

Answer 1

Answer: (B)

One

Answer 2

For an $n^{t h}$ order reaction,
$t_{1 / 2} \propto \frac{1}{C^{n-1}}$ (C =initial conc.)
Hence, for Ist order reaction $(n=1)$, we have
$t_{1/2} \propto \frac{1}{C^{1-1}}$
$\therefore t_{1 / 2} \propto C^{0}$
Thus half life of Ist order reaction is independent of the initial concentration of reactant.