MHT CET · Chemistry · Chemical Kinetics

The reaction \(\mathrm{N}_{2} \mathrm{O}_{5} \longrightarrow 2 \mathrm{NO}_{2}+\frac{1}{2} \mathrm{O}_{2}\) is first order in \(\mathrm{N}_{2} \mathrm{O}_{5}\) having rate constant \(6 \cdot 2 \times 10^{-4} \mathrm{~s}^{-1} .\) What is the value of rate of reaction when concentration of \(\mathrm{N}_{2} \mathrm{O}_{5}\) is \(1 \cdot 25 \mathrm{~mol} \mathrm{~L}^{-1}\) ?

A \(7 \cdot 75 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}\)
B \(8 \cdot 15 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}\)
C \(4 \cdot 96 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}\)
D \(2 \cdot 01 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(7 \cdot 75 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}\)

Step-by-step Solution

Detailed explanation

\(
\mathrm{N}_{2} \mathrm{O}_{5} \longrightarrow 2 \mathrm{NO}_{2}+\frac{1}{2} \mathrm{O}_{2}
\)
For first order reaction,
\(
\begin{aligned}
\text { Rate } &=\mathrm{k}\left[\mathrm{N}_{2} \mathrm{O}_{5}\right] \\
&=6.2 \times 10^{-4} \mathrm{~s}^{-1} \times 1.25 \mathrm{~mol} \mathrm{~L}
\end{aligned}
\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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