Final answer:
The different enthalpy of vaporization values among butanol isomers are due to variations in their intermolecular forces, notably hydrogen bonding and dispersion forces. The molecular size and structural configurations also affect the extent of these forces, causing different ΔHvap.
Step-by-step explanation:
The differences in the enthalpy of vaporization (ΔHvap) among butanol isomers can be attributed to the variations in strength of their intermolecular forces (IMFs). These compounds all exhibit hydrogen bonding, which is a notably strong IMFs that are difficult for the molecules to overcome. This results in relatively low vapor pressures. As the molecular size increases from methanol to butanol, the strength of dispersion forces also increases, contributing to the decrease in vapor pressure across this series: Pmethanol > Pethanol > Ppropanol > Pbutanol. The diversity in the structural configurations of butanol isomers leads to different contact areas between molecules, thus affecting the extent of dispersion forces and resulting in varying ΔHvap.