Question

Ellingham diagram represents change of:
A. $\Delta G$ with temperature
B. $\Delta H$ with temperature
C. $\Delta G$ with pressure
D. $\left( {\Delta G\; - T\Delta S} \right)$ with temperature

Answer 1

The basis of the variation of the reaction at a particular temperature is the Gibbs free energy which must be negative in the whole reaction.

Complete step by step solution
We know that, the Ellingham diagram is a graphical representation showing the relationship between the $\Delta{{_f}G}$ and $T$ for the formation of various elements i.e. the Ellingham diagram is a graph plotted between $\Delta{{_f}G}$ Vs $T$. Ellingham diagram has its application in the field of metallurgy.

We know that;
$\Delta G = \Delta H - T\Delta S$, where $\Delta G$ is Gibbs free energy, H is the enthalpy and T is temperature.

Also, when we plot a graph between ΔG and T the graph obtained will be a straight line. The slope of this graph depends upon ΔS.

Ellingham diagram tells us about the spontaneity of the reaction. As temperature increases the thermal stability of the oxides decreases as $\Delta G$ increases.

So, we can conclude that Ellingham diagram depicts the temperature dependence of the
stability of the compounds. Also, the Ellingham diagram tells us about the melting point of the metal. The abrupt change in the slope of the line represents the phase transition i.e. melting of the metal. And thus, the temperature at this point represents the melting point of the metal.

In addition to these the Ellingham diagram predicts the possibility of the reduction of a metal oxide with other metal. According to the Ellingham diagram the metal whose plot is below can reduce the metal oxide of the metal whose graph is above it.

**Hence, option (A) $\Delta G$ with temperature, is the correct option.

Note:**
Thus, Ellingham diagram is a graphical representation between $\Delta G$ and temperature. Ellingham diagram tells us about “the temperature dependence of the stability of the compounds”.