CO₂ has a positive slope on the melting (fusion) curve. Using the questions below as a guide, show that CO2 expands upon melting, without employing the Clausius-Clapeyron equation.
(i) Sketch the specific Gibbs free energies of both phases as a function of pressure using the p-T phase diagram. Use derivatives of the specific Gibbs free energies to obtain the sketch.
(ii) Sketch the specific volumes of both phases as a function of pressure.
(iii) Explain how you obtained the sketch of the specific volumes, hence show that CO2 expands upon melting.