A closed, rigid container holds pure liquid ethanol at its normal freezing point. Laboratory refrigeration equipment is programmed to remove exactly 15.0 kJ of energy from the system while the pressure remains constant at 1 atm. The molar enthalpies of phase change for ethanol are
• fusion: 5.02 kJ mol⁻¹ (melting or freezing)
• vaporization: 38.6 kJ mol⁻¹ (boiling or condensing)
No temperature change is observed during the energy removal process.
(a) Explain why the temperature of the ethanol remains constant even though energy is being removed from the system.
(b) Identify the signs (positive or negative) of q and ΔH for the ethanol during this process, and justify your answers in terms of the direction of energy transfer.
(c) The molar enthalpy of vaporization is significantly larger than the molar enthalpy of fusion for ethanol. Describe, on the particulate level, why more energy is required for vaporization than for fusion.