Question

The half life period of a substance is $50$ minutes at a certain initial oncentration. When concentration is reduced to one-half, half life is found to $25$ minutes. Order of reaction is

• A. Zero
• B. First
• C. Second
• D. Third

Answer 1

Answer: (A)

$t_{1 / 2} \propto a^{1-n}$
$\frac{\left(t_{1 / 2}\right)_{1}}{\left(t_{1 / 2}\right)_{2}}=\left(\frac{a_{1}}{a_{2}}\right)^{1-n} \rightarrow\left(\frac{50}{25}\right)=\left(\frac{a}{\frac{1}{2} a}\right)^{1-n}$
$(2) \Rightarrow (2)^{1-n}$
$\therefore n=0$
$(2)=(2)^{1-0}$