# Ethanol (C₂H₅OH) is a simple molecular substance that is liquid at room temperature. It has a boiling point of 78 °C. Pentane (C₅H₁₂) is also a simple molecular substance but has a boiling point of 36 °C. Explain why both ethanol and pentane have relatively low boiling points, and suggest why ethanol has a higher boiling point than pentane despite having fewer electrons.

> Edexcel A-Level Chemistry (9CH0) — 2.4 Forces between molecules · Explain · 5 marks

> Ethanol has the molecular formula C₂H₅OH and a boiling point of 78 °C. Pentane has the molecular formula C₅H₁₂ and a boiling point of 36 °C. Both are simple molecular substances.

## Mark scheme (5 marks)

1. Simple molecular substances have weak intermolecular forces between molecules
2. Only a small amount of energy is needed to overcome these weak intermolecular forces
3. Therefore the boiling point is low / the substance boils at a low temperature
4. Ethanol can form hydrogen bonds between its molecules (due to the OH group), which are stronger than the intermolecular forces in pentane
5. More energy is needed to overcome the stronger intermolecular forces in ethanol, so its boiling point is higher than pentane's

## Key terms

- [simple molecular substance](https://www.gradenine.co.uk/glossary/simple-molecular-substance)
- [boiling point](https://www.gradenine.co.uk/glossary/boiling-point)

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Source: [GradeNine](https://www.gradenine.co.uk/q/ethanol-c-h-oh-is-a-simple-molecular-c8d37f80) · Published by Druglandscape Ltd.