Question

The rate of the first-order reaction $X\to$ products is $7.5 \times 10^{-4} mol L^{-1} min^{-1.}$ What will be the value of rate constant when the concentration of $X$ is $0.5\, mol\, L^{-1}?$

• A. $3.75 \times 10^{-4} s^{-1}$
• B. $2.5 \times 10^{-5} s^{-1}$
• C. $1.5 \times 10^{-3} s^{-1}$
• D. $8.0 \times 10^{-4} s^{-1}$

Answer 1

Answer: (B)

Rate of reaction $=7.5\times10^{-4} molL^{-1}min^{-1}$
$=\frac{7.5\times10^{-4}}{60}mol L^{-1}s^{-1}$
$=1.25\times10^{-5}mol\, L^{-1}sec^{-1}$
Rate of reaction$=k\left[concentration \,of\, reactant\, X\right]$
or $k=\frac{1.25\times10^{-5} }{0.5}=1.25\times10^{-5}s^{-1}$