COMEDK · Chemistry · 19. Chemical Kinetics

Which one of the following is incorrect?

A Larger the value of rate constant \((\mathrm{k})\) value faster is the chemical reaction.
B The unit for rate constant for \(\mathrm{n}^{\text {th }}\) order reaction is \(\left(\mathrm{mol} \mathrm{L}^{-1}\right)^{\mathrm{n}-1} \mathrm{~s}^{-1}\)
C Rate constant equals the rate of reaction when concentration of reactants equals unity.
D The value of rate constant \((k)\) is independent of concentration of reactants.

Verified Solution

Answer & Solution

Correct Answer

(B) The unit for rate constant for \(\mathrm{n}^{\text {th }}\) order reaction is \(\left(\mathrm{mol} \mathrm{L}^{-1}\right)^{\mathrm{n}-1} \mathrm{~s}^{-1}\)

Step-by-step Solution

Detailed explanation

For an \(n^{th}\) order reaction: Rate \(= k[\text{Reactant}]^n\) Unit of \(k = \dfrac{\text{mol } L^{-1} s^{-1}}{(\text{mol } L^{-1})^n} = (\text{mol } L^{-1})^{1-n} s^{-1}\) Option (2) states the exponent as \((n-1)\) instead of the correct \((1-n)\), making it incorrect. (1)…

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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