IEMJEE Chemistry preparation: Chemical first-order half-lives — worked example and reasoning

Problem to solve

For k=0.1 s⁻¹, find half-life.

Try the problem before reading the answer. Record the requested quantity, relevant information and any interpretation choices. Keep this original practice example separate from official examination questions or previous-year papers.

Choose the governing principle

t₁/₂=ln2/k.

In a first-order kinetic model, each halving takes the same time even though the amount consumed shrinks.

Worked answer

0.693/0.1=6.93 s.

The answer follows the stated model and the values in this question. Preserve exact expressions when given; if you use a numerical approximation, label it and keep sufficient precision until the final step.

Audit the reasoning

Check atom and charge bookkeeping, units, signs and the identity of the species to which a statement applies. For an organic transformation, retain the substrate and conditions. A familiar reagent or periodic trend is not enough to prove every proposed product or comparison.

A specific error to avoid here: The constant half-life result is specific to the first-order model, not all reaction orders.

Explain before repeating

Write a short explanation linking the governing principle to the answer rather than copying the final line. Identify one assumption and explain how violating it would make this method unreliable. Use the linked worksheet for a new task, then return to this example after a delay and solve it without the answer visible.

Official sources and verification

Sources checked on 26 October 2026. A source’s date, programme and campus limit which claims it supports. Official pages may change after review.

1. UEM — IEMJEE examination information

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2. NTA — explicitly labelled JEE Main 2026 syllabus

   Historical PCM syllabus reference. Lessons and exercises are independently authored, not official IEMJEE papers or verified 2027 paper predictions.

3. NCERT — official textbook catalogue

   Primary textbook reference for checking school-level concepts. This directory does not certify the independent lesson or establish IEM examination weightage.

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