Question

The concentration of a reactant X decreases from 0.1 M to 0.005 M in 40 min. If the reaction follows first order kinetics, the rate of the reaction when the concentration of X is 0.01 M will be

• A. $ 1.73\times {{10}^{-4}}\,M\,{{\min }^{-1}} $
• B. $ 3.47\times {{10}^{-4}}\,M\,{{\min }^{-1}} $
• C. $ 3.47\times {{10}^{-5}}\,M\,{{\min }^{-1}} $
• D. $ 7.5\times {{10}^{-4}}\,M\,{{\min }^{-1}} $

Answer 1

Answer: (D)

$ k=\frac{2.303}{t}\log \frac{{{A}_{0}}}{A} $ $ =\frac{2.303}{40}\log \frac{0.1}{0.005} $ $ =\frac{2.303}{40}\log 20 $ $ =0.075 $ Rate of reaction when concentration of X is 0.01 M will be $ 0.075\times 0.01=7.5\times {{10}^{-4}}M\text{ }{{\min }^{-1}} $