CAIE A-Level Chemistry 23.4.1 The Gibbs Equation

Practise stating and rearranging ΔG° = ΔH° − TΔS° with consistent energy units and kelvin temperature.

Exam points

state ΔG° = ΔH° − TΔS° and identify ΔG° as standard Gibbs free-energy change
use T in kelvin and convert entropy units so TΔS has the same units as ΔH and ΔG
rearrange the equation to find ΔH, ΔS or the temperature at which ΔG equals zero

[Maximum number: 1]

For a particular gas phase reaction the variation in standard Gibbs free energy change, $\Delta G^{\ominus}$ , with temperature is shown.

Assume standard enthalpy change, $\Delta H^{\ominus}$ , and standard entropy change, $\Delta S^{\ominus}$ , remain constant with temperature.

Figure for Question 23.4.1—The Gibbs equation ΔG question 1 — CAIE A-Level Chemistry A2

Write the equation that relates $\Delta G^{\ominus}$ to $\Delta H^{\ominus}$ and $\Delta S^{\ominus}$ .

$\Delta G^{\ominus} = \Delta H^{\ominus} - \mathrm{T}\Delta S^{\ominus}$

All question bank results loaded

23.4.1—The Gibbs equation ΔG question 1