In Ellingham Diagram, it is mentioned that when the materials melt/vaporize, the entropy change makes the slope of the graph more higher, increasing Gibbs free energy (becomes less -ve).
But, in such cases∆S becomes +ve as the randomness increase due to phase change (solid to liquid or liquid to gas), and according to the equation∆G =∆H - T∆S,∆G should become more -ve! Please explain with help of the equation and do correct my statement.
The melting or vaporisation takes place in the reactants. The product remains solid. So, although entropy increases in the reactants, the entropy of the reaction further decreases due to which there is an abrupt change in the slope of the graph at the melting point of the solid. The slope moves higher showing that G becomes more positive.