Chemistry - Metallurgy Question with Solution | TestHub

Question Explain: Select possible graph for the change in $\Delta {\mathrm{G}}^{\circ }$ against temperature in Ellingham diagram.

Concept: This question is based on Ellingham diagram

Solution:

For the reaction $2E(s)+O_2(g)\to 2EO(g)$, we need to determine the change in entropy $\Delta S^{\circ }$. The reactants include one mole of gas $O_2$, while the products include two moles of gas $2EO$.

Since the number of moles of gas increases from 1 to 2, the entropy of the system increases. Therefore, the standard entropy change is positive ($\Delta S^{\circ }>0$).

From the Gibbs-Helmholtz equation, $\Delta G^{\circ }=\Delta H^{\circ }-T\Delta S^{\circ }$.

The y-intercept of the graph corresponds to $\Delta H^{\circ }$. Since $\Delta H^{\circ }$ is negative, the line should intercept the y-axis (the $\Delta G^{\circ }$ axis) at a negative value.

The slope of the graph is equal to $-\Delta S^{\circ }$. Since $\Delta S^{\circ }$ is positive, the slope will be negative. A negative slope means the line goes downwards as temperature increases.