Physical properties
2 marks · EasyExplain why propene has a higher boiling point than ethene.
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Must show: comparison made, reason given
Also accept: Propene is a larger molecule with more electrons, so its intermolecular forces are stronger, leading to a higher boiling point.
Common mistakes: Incorrectly states ethene has more carbons; Gives only the fact, not reason
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Marking points
M1 · 1 mark · States or recognises that propene has more carbon atoms (is a bigger molecule) than ethene
A1 · 1 mark · Explains that bigger molecules have stronger (intermolecular) forces or require more energy to separate, so higher boiling point
Worked solution
Propene has more carbon atoms than ethene and is a larger molecule. Larger alkenes have stronger intermolecular forces, so propene has a higher boiling point.