AP EAMCET · Chemistry · Chemical Kinetics

If the rate constant for a first order reaction is \(k\), then find the time required for completion of \(80 \%\) of the reaction.

A \(\frac{3.2}{k}\)
B \(\frac{1.6}{k}\)
C \(\frac{4.8}{k}\)
D \(\frac{0.8}{k}\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(\frac{1.6}{k}\)

Step-by-step Solution

Detailed explanation

First order rate constant is given as \(k=\frac{2.303}{t} \log \frac{\left[A_0\right]}{\left[A_t\right]}\) \(80 \%\) completed, then \(\left[A_0\right]=100\) \(A_t=100-80=20\)…

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.

Same subject

Which of the following sets are correctly matched?

Molecule	Hybrididization	Geometry
I. \(\mathrm{BrF}_5\)	\(\mathrm{sp}^3\mathrm{d}^2\)	square pyramidal
II. \(\mathrm{XeF}_6\)	\(\mathrm{sp}^3\mathrm{d}^3\)	Distorted octahedral
III. \(\mathrm{SF}_4\)	\(\mathrm{dsp}^2\)	square planar
IV. \(\mathrm{PbCl}_2\)	sp	linear

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