It is quite common for a solid to change from one solid state structure to another at a temperature below its melting point.

Question

For example, sulfur undergoes a phase change from the α-orthorhombic form (S8; density≅2.07 g/cm3) to the β-monoclinic form (S8; density≅2.00 g/cm3) as it is warmed above 95.3 °C.
Assuming that ΔH for this phase change is 0.442 kJ/mol, calculate ΔS for this phase change.

Answer 1

For a reaction, dG = dH - TdS
Assuming the phase change is at 95.3, then dG @ equilibrium = 0. Plug in dH and T and solve for dS.