WAEC Chemistry 2020 Paper

Concept:Boiling point depends on the strength of intermolecular forces between molecules.Explanation:Pentane ($\mathrm{C}_5\mathrm{H}_{12}$) has five carbon atoms, while propane ($\mathrm{C}_3\mathrm{H}_8$) has only three carbon atoms.As the number of carbon atoms increases, the molecular size and surface area increase.This leads to stronger London dispersion forces between pentane molecules.These intermolecular forces, though weak individually, become more significant with more electrons and atoms in the molecule.More energy is required to overcome the stronger forces in pentane, so its boiling point is higher.Thus, option D correctly states that the intermolecular forces in pentane are stronger than those in propane.Answer:D. The intermolecular forces in pentane are stronger than those of propane.