Alkanes
| English | Chinese | Pinyin |
|---|---|---|
| alkane | 烷烃 | wán tīng |
| saturated | 饱和 | bǎo hé |
| hydrogenation | 氢化 | qīng huà |
| cracking | 裂化 | liè huà |
| combustion | 燃烧 | rán shāo |
| carbon monoxide | 一氧化碳 | yī yǎng huà tàn |
The unreactive backbone
- Alkanes 烷烃 are saturated 饱和 hydrocarbons ($\text{C}_n\text{H}_{2n+2}$).
- They are useful fuels but generally unreactive.
- We make them and burn them.
Alkanes are:
Alkanes have only single C–C bonds (saturated) and follow CₙH₂ₙ₊₂.
Alkanes are saturated hydrocarbons containing only single bonds.
General formula CₙH₂ₙ₊₂.
Making alkanes
- hydrogenation 氢化: add hydrogen to an alkene (Pt or Ni catalyst, heat).
- cracking 裂化: break a long-chain alkane into shorter ones (heat with $\text{Al}_2\text{O}_3$).
An alkene decolourises bromine water; an alkane does not
The tetrahedral carbon
Each carbon in an alkane has four bonding pairs and no lone pairs — they spread as far apart as possible into a tetrahedron (109.5°).
Cracking is used to:
Cracking turns heavy crude-oil fractions into smaller, more useful alkanes and alkenes.
Match each alkane fact.
Each item links the term to its correct meaning.
Combustion 燃烧
- complete (plenty of oxygen) → carbon dioxide + water.
- incomplete (not enough oxygen) → water + toxic carbon monoxide 一氧化碳 (CO) + soot.
Natural gas (mainly methane, an alkane) burns on a stove
Incomplete combustion of an alkane (not enough oxygen) produces:
With too little oxygen you get CO (toxic) and carbon (soot) as well as water.
Unreactivity and environment
- Alkanes are unreactive towards polar reagents: the C–H and C–C bonds are strong and have little polarity, so there's no charge to attract attack.
- Burning them in engines gives CO, NOₓ and unburnt hydrocarbons — a catalytic converter removes these.
Alkanes are unreactive towards polar reagents because their bonds are:
Non-polar, strong C–H and C–C bonds give no charged site for an attacking species.
You've got it
- alkanes = saturated hydrocarbons ($\text{C}_n\text{H}_{2n+2}$); made by hydrogenation or cracking
- complete combustion → CO₂ + water; incomplete → toxic CO + soot
- unreactive (strong, non-polar bonds); engine pollutants removed by a catalytic converter