Alkanes
Alkanes
- Alkanes have only single bonds → saturated hydrocarbons.
- They are generally unreactive. Two key reactions:
- Combustion: burn in plenty of oxygen → carbon dioxide + water.
- Substitution with chlorine.
Practice
Alkanes are described as saturated because they have:
Only single bonds = saturated; alkanes are generally unreactive.
Practice
Alkanes burn in plenty of oxygen to give carbon dioxide and water.
Complete combustion of an alkane gives carbon dioxide and water.
Substitution with chlorine
- In a substitution reaction, one atom is replaced by another.
- Alkanes react with chlorine only in ultraviolet light (a photochemical reaction — the light supplies the activation energy):
$$\text{CH}_4 + \text{Cl}_2 \rightarrow \text{CH}_3\text{Cl} + \text{HCl}$$
Practice
Alkanes react with chlorine only in the presence of:
The substitution is photochemical — UV light supplies the activation energy.
You've got it
Key idea
- alkanes = saturated (single bonds), generally unreactive
- they combust to CO₂ + water, and undergo substitution with chlorine
- substitution needs UV light: $\text{CH}_4 + \text{Cl}_2 \rightarrow \text{CH}_3\text{Cl} + \text{HCl}$