In a first order reaction the concentration of reactant decreases from $800 \, \text{mol/dm}^3$ to $50 \,…

In a first order reaction the concentration of reactant decreases from $800 \, \text{mol/dm}^3$ to $50 \, \text{mol/dm}^3$ in $200 \, \text{sec}$. The rate constant of reaction in $s^{-1}$ is
  1. $2 \times 10^{-4} s^{-1}$
  2. $1.386 \times 10^{-2} s^{-1}$
  3. $3.45 \times 10^{5} s^{-1}$
  4. $2 \times 10^{4} s^{-1}$

Solution

C t  =  C 0 2 n
2 n = 800 50 =16
2 n = 2 4
So, n = 4
4T 1 2  = 200 sec
T 1 2  = 50 sec
K =  0.693 T 1 2  =  0.693 50  = 1.386 ×  10 −2   sec −1

Asked in: MHT CET Full Test 4

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