Forces between moleculesAQA A-Level Chemistry: Mind map

Exam questions on Forces between molecules

1. Propane, CH₃CH₂CH₃, and ethanal, CH₃CHO, have almost the same relative molecular mass (44). Propane boils at −42 °C, whereas ethanal boils at +20 °C.
   Explain why ethanal has a higher boiling point than propane.2 marks
2. The boiling points of the hydrogen halides are: hydrogen fluoride +20 °C, hydrogen chloride −85 °C, hydrogen bromide −67 °C and hydrogen iodide −35 °C.
   Explain why the boiling point increases from hydrogen chloride to hydrogen iodide.2 marks
3. Ice floats on liquid water, and water has an unusually high boiling point of 100 °C compared with hydrogen sulfide, H₂S, which boils at −60 °C even though H₂S has a larger relative molecular mass.
   Explain why water has a much higher boiling point than hydrogen sulfide.3 marks