Paper 1 Q4 — ΔG° = −RT ln K, and yield ≠ rate

Thermodynamics vs kinetics — the sign in ΔG° = −RT ln K; equilibrium position vs rate

What the examiners said

“Some candidates showed confusion over the definition of K or omitted the negative sign from ΔG° = −RT ln K… Many candidates confused yield/equilibria and rate.”

Item 1 — the sign

A reaction has K = 100 at 298 K. What is the sign of ΔG°, and roughly its value? (R = 8.31 J mol⁻¹ K⁻¹)

Examiner report: “Candidates omitted the negative sign in ΔG° = −RT ln K.”

Item 2 — yield vs rate

Adding a catalyst to this reaction will:

Examiner report: “Many confused yield/equilibria with rate.”

Explore — K, ΔG° and the effect of a catalyst

Change K and temperature to see ΔG° = −RT ln K. Then add a catalyst and watch the rate rise while K — and the final yield — stay put.

K: 100 T (K): 298

Thermodynamics (K, ΔG°, yield) and kinetics (rate, catalysts) are separate axes. A catalyst moves only the kinetic one.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H3 Chemistry 9813 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

Made by lookang, using Claude Fable 5. More resources: iwant2study.org