Forces between moleculesAQA A-Level Chemistry: Flashcards

What these 13 flashcards ask

Name the three types of intermolecular force from weakest to strongest.
What causes an induced dipole-dipole force?
What makes induced dipole-dipole forces stronger?
Why does branching lower boiling point?
What is a permanent dipole-dipole force?
What is needed for hydrogen bonding?
Why do NH₃, H₂O and HF have anomalously high boiling points?
What is broken when water boils?
Why is ice less dense than water?
Why does boiling point rise from HCl to HI?
Why do alkanes have increasing boiling points as chain length increases?
Which has the higher boiling point: ethanol or methoxymethane?
Why can ethanal not form hydrogen bonds with itself?

Exam questions on Forces between molecules

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
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
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

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).