Question

# Calculate the entropy of fusion of a compound at 25°C given that its enthalpy of fusion...

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.

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 = qp= CpΔT Cp= 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 ΔfusH at melting temp = 32 kJ/mol.

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

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

ΔfusH = (Cp,m(solid)) ΔT + ΔfusH+ (Cp,m(liquid)) ΔT

ΔfusH =19*121+32+28*121

ΔfusH =2.299+32+3.388

ΔfusH =37.687 Kj/mol

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