MHT CET · Chemistry · Chemical Kinetics

In a first order reaction concentration of reactant decreases from 20 milli mol dm-3 to 8 milli mol dm-3 in 40 minute, find rate constant of reaction?

A 0.011 minute \(^{-1}\)
B 0.023 minute \(^{-1}\)
C 0.032 minute \(^{-1}\)
D 0.041 minute \(^{-1}\)

Verified Solution

Answer & Solution

Correct Answer

(B) 0.023 minute \(^{-1}\)

Step-by-step Solution

Detailed explanation

\(k = \frac{1}{t} \ln\left(\frac{[A]_0}{[A]}\right)\) \(k = \frac{1}{40 \text{ min}} \ln\left(\frac{20 \text{ mmol dm}^{-3}}{8 \text{ mmol dm}^{-3}}\right)\)

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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