Question

The rate constant of the reaction $2N_2O_5 \rightarrow 4NO_2 + O_2$ at $300\,K$ is $3 \times 10^{-5}\,s^{-1}$. If the rate of the reaction at the same temperature is $2.4 \times 10^{-5}\, mol\, dm^{-3}\, s^{-1}$, then the molar concentration of $N_2O_5$ is

• A. 0.4 M
• B. 0.8 M
• C. 0.04 M
• D. 0.008 M

Answer 1

Answer: (B)

0.8 M

Answer 2

Given, $k($ rate constant $)=3 \times 10^{-5} s ^{-1}$ which indicates that reaction is of first order. $\left(: \cdot\right.$ unit is $\left.s^{-1}\right)$ $\therefore r$ (rate ofreaction) $=k$ [concentration] $^{1}$ $\therefore$ [ concentration ]$=\frac{r}{k}$ [ concentration ]$=\frac{2.4 \times 10^{-5}}{3.0 \times 10^{-5}}=0.8\, M$