FRQ — Chemical Thermodynamics

Case study·Standard multi-step (3/5)·Calculator allowed

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 student compares two gas reactions at

298\text{ K}

. Reaction P has

\Delta U=-90.0\text{ kJ mol}^{-1}

and

\Delta n_g=+1

. Reaction Q has

\Delta U=-90.0\text{ kJ mol}^{-1}

and

\Delta n_g=-1

. Use

R=8.314\text{ J mol}^{-1}\text{ K}^{-1}

Total: 5 marks

(a) Write the relation between $\Delta H$ and $\Delta U$ . (1 mark)

(b) Estimate $\Delta H$ for reaction P in kJ mol $^{-1}$ . (2 marks)

Your response (optional — you can also work on paper)

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