Question

The rate of a first order reaction $R\to P$is $7.5\times {10}^{-4}mol{L}^{-1}{s}^{-1}$ when the concentration of R is 0.5 mol $L^{-1}$.

The rate constant is

• A. $2.5\times {10}^{-5}{s}^{-1}$
• B. $1.5\times {10}^{-3}{s}^{-1}$
• C. $4.16\times {10}^{-7}{s}^{-1}$
• D. $1.5\times {10}^{-5}{s}^{-1}$

Answer 1

The correct option is A $2.5\times {10}^{-5}{s}^{-1}$

$Rate=7.5\times {10}^{-4}mol{L}^{-1}min-1=\frac{7.5\times {10}^{-4}}{60}mol{L}^{-1}{s}^{-1}$
Rate = k[R]
$\Rightarrow k=\frac{Rate}{\left[R\right]}=\frac{7.5\times {10}^{-4}}{60\times 0.5}=2.5\times {10}^{-5}{s}^{-1}$