Problem 5 - Entrance Test

Boiling point is primarily determined by the strength of intermolecular forces (IMFs). 1. CH4 (Methane): Nonpolar molecule, only exhibits weak London Dispersion Forces (LDF). Its molar mass is 16 g/mol. 2. H2S (Hydrogen Sulfide): Polar molecule, exhibits LDF and Dipole-Dipole interactions. Its molar mass is 34 g/mol. 3. H2O (Water): Highly polar molecule, exhibits LDF, Dipole-Dipole interactions, and very strong Hydrogen Bonding due to the presence of highly electronegative oxygen bonded to hydrogen. Its molar mass is 18 g/mol. Hydrogen bonds are significantly stronger than dipole-dipole interactions, which in turn are stronger than LDF (for comparable molecular sizes, though H2O also has stronger LDF than CH4 due to more electrons). Despite H2S having a higher molecular weight than H2O, the extensive hydrogen bonding in water leads to a much higher boiling point. Thus, the order of increasing boiling points is CH4 < H2S < H2O.