IEMJEE Chemistry preparation: Reaction enthalpy and Hess law — practice worksheet with answers

How to use this worksheet

This independent worksheet checks reaction enthalpy and hess law with a new problem, an explanation task and an interleaved related skill. It is not an official IEM question paper, a difficulty forecast or a prescribed timed examination.

Write an attempt first, then compare your method with the visible answers. Record whether a miss came from interpretation, a missing concept, execution or a condition you overlooked.

Question 1: apply the topic

What is ΔH for C→A?

Answer and checking point

Reverse the overall reaction: +15 kJ.

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.

Question 2: diagnose an approach

Explain why the following warning matters and identify the correction it calls for: Reversing an equation without changing the sign of its enthalpy breaks the energy bookkeeping.

Model checkpoint: Enthalpy is a state function, so a reaction's enthalpy change can be obtained by combining other reactions consistently. Governing rule: Reverse a reaction to reverse ΔH; multiply its equation to multiply ΔH.

Question 3: transfer to molar concentration

How many moles are in 250 mL of a 2 mol/L solution?

Answer: V=0.250 L, so n=2×0.250=0.5 mol.

This is an interleaved related-skill task, not a claim that the two topics have identical methods. Explain which idea changes when switching from the main topic to this one.

Review the attempt

Separate correct answers reached with a justified method from lucky guesses. Rework missed steps without looking at the answer, then use a fresh problem from an appropriate primary textbook or official paper. Do not use a small worksheet result as an admission cutoff, rank or readiness guarantee.

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

   Historical examination pattern; verify the current cycle on the central portal.

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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