The table lists enthalpy changes for several phase changes of a pure substance under 1atm pressure.
Process ΔH (kJmol−1)
A Fusion at the normal melting point +9.7
B Vaporization at the normal boiling point ?
C Sublimation at −10∘C +37.4
The substance exhibits no solid–solid polymorph transitions.
(a) Determine the numerical value of ΔH for Process B. Show your reasoning.
(b) Rank Processes A, B, and C from greatest to least magnitude of molar energy absorbed. Include the appropriate sign with each ΔH value.
(c) When 2.00mol of the substance is converted directly from solid at −10∘C to liquid at the melting point via heating, describe qualitatively how the total energy absorbed compares with the energy listed for any single process in the table. Support your answer with reasoning based on the data provided.