MHT CET · Chemistry · Chemical Kinetics

For the reaction,
\(
\mathrm{CH}_3 \mathrm{Br}_{(\mathrm{aq})}+\mathrm{OH}_{(\mathrm{sq})}^{-} \rightarrow \mathrm{CH}_3 \mathrm{OH}_{(\mathrm{aq})}+\mathrm{Br}_{(\mathrm{aq})}^{-}
\)
the rate law is rate \(=\mathrm{k}\left[\mathrm{CH}_3 \mathrm{Br}\right][\mathrm{OH}]\). What is change in rate of reaction if concentration of both reactants is doubled?

A Rate increases by factor 2
B Rate increases by factor 4
C Rate remains same
D Rate decreases by factor 2

Verified Solution

Answer & Solution

Correct Answer

(B) Rate increases by factor 4

Step-by-step Solution

Detailed explanation

Rate \(=\mathrm{k}\left[\mathrm{CH}_3 \mathrm{Br}\right][\mathrm{OH}]\)
\((\text { Rate })_1=\mathrm{k} \times 2\left[\mathrm{CH}_3 \mathrm{Br}\right] \times 2\left[\mathrm{OH}^{-}\right]\)
\(=4 \mathrm{k}\left[\mathrm{CH}_3 \mathrm{Br}\right][\mathrm{OH}]\)
\(\therefore \quad \frac{\text { (Rate })_1}{\text { Rate }}=\frac{4 \mathrm{k}\left[\mathrm{CH}_3 \mathrm{Br}\right]\left[\mathrm{OH}^{-}\right]}{\mathrm{k}\left[\mathrm{CH}_3 \mathrm{Br}\right]\left[\mathrm{OH}^{-}\right]}=4\)
\(\therefore \quad(\text { Rate })_1=4 \times\) Rate

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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