One mole of naphthalene (C₁₀H₈) is taken from 25 °C to 100 °C by the following sequence:
Step 1: Heat the solid from 25 °C to its melting point, 80 °C.
Step 2: Melt the solid completely at 80 °C.
Step 3: Heat the resulting liquid from 80 °C to 100 °C.
Relevant data (assume temperature-independent heat capacities over the ranges stated):
• C_p(s) = 125 J mol⁻¹ K⁻¹ for solid naphthalene
• C_p(l) = 150 J mol⁻¹ K⁻¹ for liquid naphthalene
• ΔH_fus = 19.1 kJ mol⁻¹ at 80 °C
(a) Calculate the entropy change for Step 1.
(b) Calculate the entropy change for Step 2.
(c) Calculate the entropy change for Step 3.
(d) Determine the total entropy change for the overall process, and comment on how the phase change contributes relative to the heating steps.