Question

In the first order reaction, 75% of the reactant gets disappeared in 1.386 h. The rate constant of the reaction is:

• A. $3.0\times {10}^{-3}{s}^{-1}$
• B. $2.8{\times 10}^{-4}{s}^{-1}$
• C. $17.2{\times 10}^{-3}{s}^{-1}$
• D. $1.8{\times 10}^{-3}{s}^{-1}$

Answer 1

The correct option is B $2.8{\times 10}^{-4}{s}^{-1}$

For a first-order reaction, the rate constant will be

$k=\frac{2.303}{t}\log \frac{a}{a-x}$

where,

K is rate constant.

t is time taken for x amount of reactant to convert to products.

a is initial concentration of reactant.

$t=1.386\times 60\times 60sec$

$x=0.75a$

$k=\frac{2.303}{1.386\times 60\times 60}\log \frac{a}{a-0.75a}$

$⟹k=\frac{2.303}{1.386\times 3600}\times \log 4=2.8\times {10}^{-4}$