Question

On the basis of Ellingham diagram which of the following is/are correct?

• A. The slope of the curve is positive until there is a phase change
• B. Above the $\Delta G=0$ line, oxide decomposes into metal & oxygen
• C. If randomness increases, the slope will increase
• D. All of these

Answer 1

The correct option is D All of these

(A) $\Delta G=\Delta H-T\Delta S$

The slope of the curve is positive because entropy decreases in the formation of oxide (loss of gaseous oxygen)
$M+\frac{1}{2}{O}_2\to MO$

(B) Above $\Delta G=0$ line, the free energy of formation of oxides is positive and the oxide is unstable and decomposes to metal and oxide.

(C) The increase of randomness is due to the vaporisation of the metal. So the entropy of the reaction decreases and hence the slope $-\Delta S$ increases.

Hence all the statements are true.