Propane and octane are both alkanes. Octane molecules have longer chains than propane molecules.
Why does the longer chain make the intermolecular forces between octane molecules stronger?
Each octane molecule has a larger surface area, so it reacts with its neighbours more readily.
Neighbouring octane molecules move faster, so they collide with each other more often.
Neighbouring octane molecules have a larger surface area in contact with each other.
Octane molecules contain double bonds that attract neighbouring molecules more strongly.
131 exam-style questions on OCR GCSE Chemistry 6.2 Organic chemistry, covering 6.2.1 Crude oil and fractional distillation, 6.2.2 Cracking and dependence on hydrocarbons, 6.2.3 Functional groups and homologous series, 6.2.4 Reactions of alkanes, alkenes and alcohols, 6.2.5 Addition polymerisation and repeat units, 6.2.6 Naturally occurring polymers, 6.2.7 Chemical cells and fuel cells, and 6.2.8 Condensation polymerisation and how to make one. Each one has a worked solution and a mark scheme showing where the marks go.