2025 H2 Chem P2 Q5: Gibbs Free Energy Solution

The effect of increasing temperature on \(\Delta G\) per mole of \(O_2\) reacted for reaction 2 is shown in Fig. 5.1.

reaction 2 \(2Mg(s) + O_2(g) \rightarrow 2MgO(s)\)

State the equation that relates the value of \(\Delta G\) to the values of \(\Delta S\) and \(\Delta H\).

Use Fig. 5.1 to deduce the value of \(\Delta S\) for reaction 2. Include relevant units in your answer.

On Fig. 5.1, show how the value for \(\Delta H\) for reaction 2 can be determined.

The effect of increasing temperature on \(\Delta G\) per mole of \(O_2\) reacted for reaction 3 and reaction 4 is shown in Fig. 5.2.

reaction 3 \(2Cu(s) + O_2(g) \rightarrow 2CuO(s)\)
reaction 4 \(\tfrac{4}{3}Al(s) + O_2(g) \rightarrow \tfrac{2}{3}Al_2O_3(s)\)

Hess' Law can be used to construct simple cycles involving values for Gibbs free energy change, \(\Delta G\), in a similar way to cycles involving values for \(\Delta H\).

Using the data shown about reaction 3 and reaction 4 in Fig. 5.2, calculate the value of \(\Delta G\) for the formation of 1 mol of Cu when CuO reacts with an excess of Al at 300 K.