Physical properties
3 marks · EasyDescribe the physical state of ethene, propene and butene at room temperature.
Explain how the boiling points of these alkenes change as the number of carbon atoms increases.
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(a) They are gases.
(b) Boiling point increases as the number of carbon atoms increases (from ethene to butene) · must show trend stated, correct explanation (e.g. more intermolecular forces)
Common mistakes: Alkenes are liquids/gases at wrong state; Incorrect direction of boiling point trend
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Marking points
B1 (a) · 1 mark · States that all (C2–C4) alkenes are gases at room temperature
M1 (b) · 1 mark · States or describes the trend that boiling point increases as number of carbon atoms increases
A1 (b) · 1 mark · Explains the reason for the trend (e.g., stronger intermolecular forces, more electrons, larger molecules)
Worked solution
(a) Ethene, propene and butene are all gases at room temperature.
(b) The boiling point of alkenes increases as the number of carbon atoms increases, because the molecules get bigger and the intermolecular forces become stronger.