Question

In a 1st order reaction A $\to$ products, the concentration of the reactant decreases to 6.25$\%$ of its initial value in 80 minutes. What is (i) the rate constant and (ii) the rate of reaction, 100 minutes after the start, if the initial concentration is 0.2 mole/litre?

• A. $2.17\times {10}^{-2}mi{n}^{-1},3.47\times {10}^{-4}mol.litr{e}^{-1}mi{n}^{-1}$
• B. $3.465\times {10}^{-2}mi{n}^{-1},2.166\times {10}^{-4}mol.litr{e}^{-1}mi{n}^{-1}$
• C. $3.465\times {10}^{-3}mi{n}^{-1},2.17\times {10}^{-3}mol.litr{e}^{-1}mi{n}^{-1}$
• D. $2.166\times {10}^{-3}mi{n}^{-1},2.667\times {10}^{-4}mol.litr{e}^{-1}mi{n}^{-1}$

Answer 1

The correct option is B $3.465\times {10}^{-2}mi{n}^{-1},2.166\times {10}^{-4}mol.litr{e}^{-1}mi{n}^{-1}$

$T_{1/2}=\frac{80}{4}=20minK=\frac{0.693}{20}=3.465\times {10}^{-2}[A{]}_{100}=\frac{0.2}{25}=\frac{0.2}{32}=0.00625R_{100}=3.465\times {10}^{-2}\times 0.00625=2.166\times {10}^{-4}$