Solid carbon dioxide (dry ice) undergoes sublimation at −78.5 °C and 1 atm. The molar enthalpy of fusion of CO₂ is 9.0 kJ mol⁻¹ and its molar enthalpy of vaporization is 16.3 kJ mol⁻¹ at the same temperature. A datasheet lists the molar enthalpy of sublimation of CO₂ as 25.2 kJ mol⁻¹.
(a) Using the data provided, calculate a theoretical value for the molar enthalpy of sublimation for CO₂ at −78.5 °C. Show all work and include units.
(b) Compare your calculated value from part (a) with the value reported in the datasheet. Provide one plausible reason for any discrepancy observed.
(c) Classify the sublimation of CO₂ as a physical change, a chemical change, or both. Justify your answer by discussing the types of interactions altered during the process and relating them to your enthalpy calculations.
(d) Predict qualitatively how the sign and magnitude of the entropy change (ΔS) for the sublimation of CO₂ would compare with that for the fusion of CO₂. Support your prediction with molecular reasoning.