Crude oil is a finite resource that is separated into fractions by fractional distillation. Explain why crude oil is described as a finite resource and outline two environmental problems caused by the combustion of hydrocarbon fuels obtained from crude oil.

Crude oil is a finite resource because it was formed over millions of years from the remains of ancient organisms and it cannot be replaced on a human time‑scale; therefore it will eventually run out.

The combustion of hydrocarbon fuels from crude oil causes two main environmental problems:
1. Complete combustion releases carbon dioxide, a greenhouse gas that drives global warming and climate change.
2. Combustion of sulphur‑containing hydrocarbons produces sulphur dioxide, which leads to acid rain. Incomplete combustion can also give rise to carbon monoxide and particulates, which contribute to air‑quality problems and health hazards.