Iodine undergoes the following phase changes at 184 °C:
• solid → liquid, molar enthalpy 15.5 kJ mol⁻¹
• liquid → gas, molar enthalpy 41.6 kJ mol⁻¹
A chemist plans to convert a 50.0 g sample of solid iodine at 184 °C directly to gaseous iodine at the same temperature and later allow the vapor to deposit back to solid.
(a) Determine the molar enthalpy for the overall direct solid-to-gas transition (sublimation) of iodine at 184 °C. Include the correct sign.
(b) Calculate the total heat, in kJ, required to sublime the 50.0 g sample of iodine at 184 °C.
(c) After sublimation, the gaseous iodine is allowed to deposit fully back to the solid at 184 °C. Quantitatively compare the heat change for deposition to that for sublimation and explain how this comparison illustrates the principle of energy conservation in phase transitions.