Water (H2O\text{H}_2\text{O}H2O) is a liquid at room temperature with a boiling point of 100∘C100^\circ\text{C}100∘C, whereas hydrogen sulfide (H2S\text{H}_2\text{S}H2S) is a toxic gas with a boiling point of −60∘C-60^\circ\text{C}−60∘C, despite hydrogen sulfide having a larger molecular mass.
Which statement correctly explains this difference in boiling points?
The covalent O−H\text{O}-\text{H}O−H bonds within water molecules are significantly stronger than the S−H\text{S}-\text{H}S−H covalent bonds in hydrogen sulfide, requiring more energy to break during boiling.
Water molecules can form strong intermolecular hydrogen bonds, whereas hydrogen sulfide molecules can only form weaker dipole-dipole and London dispersion forces.
Water forms a giant covalent macromolecular network at room temperature, whereas hydrogen sulfide exists as a simple molecular structure.
The larger molecular mass of hydrogen sulfide increases the strength of its London dispersion forces, which causes the molecules to repel one another and lowers the temperature needed to vaporise.
74 exam-style questions on OCR GCSE Chemistry Bonding. Each one has a worked solution and a mark scheme showing where the marks go.