Question

At standard pressure, CH4 boils at 112 K and H2O boils at 373 K. What accounts for the higher boiling point of H2O at standard pressure?
(1) covalent bonding (3) hydrogen bonding(2) ionic bonding (4) metallic bonding

Answer 1

The answer is (3) hydrogen bonding. This is a question of intermolecular forces. H2O is highly polar (the O—H bond is particularly polar since O is so electronegative), and CH4 is about as nonpolar as it gets. So, while H2O molecules are held together by relatively strong hydrogen bonds (which, keep in mind, are not actually bonds), CH4 molecules are held together by much weaker London dispersion/Van der Waals forces. Thus, it takes more thermal energy to separate H2O molecules, and H2O therefore has a higher boiling point.