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Case study·Standard multi-step (3/5)·No calculator

Difficulty guide

The label describes the problem, not your ability.

1/5 - Foundational

Warm-up setup; checks one basic idea.

2/5 - Routine exam skill

Normal syllabus skill; usually one main rule or interpretation.

3/5 - Standard multi-step

Exam-style problem with multiple steps or a common trap.

4/5 - Hard exam skill

High-end exam problem; combines methods carefully.

5/5 - Challenge

Stretch problem beyond normal exam pressure.

Question

A medicine decomposes approximately by first-order kinetics. At 298 K298\,\mathrm{K}, k=0.010 day−1k=0.010\,\mathrm{day^{-1}}. Its activation energy is about 48 kJ mol−148\,\mathrm{kJ\,mol^{-1}}. When stored at 308 K308\,\mathrm{K}, the rate constant becomes about 1.91.9 times larger.
Total: 4 marks

(a) Calculate the half-life at 298 K298\,\mathrm{K}. (1 mark)

(b) Estimate kk at 308 K308\,\mathrm{K}. (1 mark)

(c) Estimate the half-life at 308 K308\,\mathrm{K}. (1 mark)

(d) State why warmer storage shortens shelf life. (1 mark)

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cbse-chemistry-12.u3.t3-4.case.005

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