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)

$t_{1/2}\propto a^{1-n}$
$\frac{{\left(t_{1/2}\right)}_1}{{\left(t_{1/2}\right)}_2}={\left(\frac{a_1}{a_2}\right)}^{1-n}\to \left(\frac{50}{25}\right)={\left(\frac{a}{\frac{1}{2}a}\right)}^{1-n}$
$(2)\Rightarrow (2{)}^{1-n}$
$\therefore n=0$
$(2)=(2{)}^{1-0}$