A reaction has dH = +40.0 kJ/mol and dS = +120 J/K/mol. Calculate the minimum temperature for feasibility and dG at 350 K.
[4 marks]
Total for this question: 4
All calculations
Gibbs free energy and feasibility
Thermodynamics
AQA 7405
ORIGINAL
dG = dH - T dS
Entropy is commonly in J/K/mol while enthalpy is in kJ/mol; align the units before multiplying by temperature.
Board and spec code confirmed against AQA 7405 · registry checked 2026-07-11How this checking works
Work it, then mark it
Do each calculation on paper first, then reveal the mark scheme and tick the marks you actually earned — the same way you should mark past papers.
Q1
Do the calculation on paper first — then mark it.
Where the marks get lost
- Mixing joules and kilojoules.
- Treating a negative dG as proof that the reaction will be fast.
Exam tip: A negative dG predicts thermodynamic feasibility, not reaction rate; kinetics is a separate question.
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