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Question
Why ethanol has the higher boiling point than ethane?
Solution
1) Alcohol has higher boiling points than their corresponding alkanes due to the presence of intermolecular hydrogen bonding which is absent in the alkanes.
2) Hydrogen bonding arises due to the presence of electronegative atom oxygen in –OH group of the alcohol.
3) Oxygen atom attracts electron density of O–H bond towards itself and hence it gets the partial negative charge, while H atom gets partial positive change.
`-delta + delta`
R-O-H
4) Hence in alcohol, R–OH molecules become polar
5) There arises strong intermolecular attraction between the oxygen atom of one molecule of alcohol and ‘H’ atom of another alcohol molecule, giving rise to strong hydrogen bonding which is not present in alkanes.
6) Hence higher thermal energy is required to separate or evaporate alcohol molecule. Therefore alcohols have higher boiling points than their corresponding alkanes.
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