Chemistry Question?

Question

It is quite common for a solid to change from one solid state structure to another at a temperature below its melting point. For example, sulfur undergoes a phase change from the rhombic crystal structure to the monoclinic form at 95.3oC. Assuming that ΔHo for this phase change is 0.490 kJ/mol, calculate ΔSo for this phase change.

Answer 1

Lancenigo di Villorba (TV), Italy

THE ANSWER IS +1.33 J/(mol * K).

Your trouble lies its referee about ALLOTROPIC EQUILIBRIA.
I remember you that ALLOTROPY is the phenomenon shown by some Chemical Elements when it may exists in several AGGREGATION's SOLID STATEs.
Thus, I am treating on SOLID STATE's EQUILIBRIA, e.g. Rhombic and Monoclinic Forms for Sulphur

S(rhombic) <---> S(monoclinic)

The UNDEFINED GIBB's EQUATION is

DeltaG° = DeltaH° - T * DeltaS°

where "DeltaG°" is the GIBB FREE ENERGY's CHANGE along the overwritten reaction when it is studied at the standard conditions ; similarly, there are also "DeltaH°" and "DeltaS°" which are respectively the ENTHALPY's CHANGE and the ENTROPY's One.
You wrote that the ALLOTROPIC EQUILIBRIUM occurs
at 1 atm and 95.3 °C = 368.5 K, e.g. I retrieve Equilibrium Conditions or DeltaG° = 0.0 kJ/mol

0.0 = DeltaG° = DeltaH° - T * DeltaS°
DeltaS° = DeltaH° / T = 490 / 368.5 = 1.33 J/(mol * K)

I hope this could be clear.

Answer 2

delta H = T x delta S

So delta S = delta H/T

Set delta H to 490 to match the units of S, and you're away!