Question

Calculate the entropy of fusion of a compound at 25°C given that

its enthalpy of fusion is 32 kJ mol−1 at its melting point of 146°C and

the molar heat capacities (at constant pressure) of the liquid and solid

forms are 28 J K−1 mol−1 and 19 J K−1 mol−1, respectively.

Answer 1

Given that the entropy of fusion at 25.0°C can be calculated by using the enthalpy of fusion at 25.0°C, which is determined by the following path.

1) Heating in the solid phase from 25°C to 146°C.

Will use ΔH = q_p= C_pΔT C_p= 19 J K^-1mol^-1( (19*121)/1000) Converting it in Kj/mol

2) Phase transition from solid to liquid at 146°C

Will use Δ_fusH at melting temp = 32 kJ/mol.

3) Cooling in the liquid phase to 146°C →25°C

Will use ΔH = q_p= C_pΔT   Cp= 28 J K^-1mol^-1((28*121)/1000) Converting it in Kj/mol

Δ_fusH = (C_p,_m(solid)) ΔT + Δ_fusH+ (C_p,_m(liquid)) ΔT

Δ_fusH =19*121+32+28*121

Δ_fusH =2.299+32+3.388

Δ_fusH =37.687 Kj/mol