VCE Chemistry

## What a fuel is A **fuel** is a substance that reacts to release useful energy, most often as heat, and in practice nearly always by combustion with oxygen. The fuels met in VCE Chemistry are carbon-based and fall into two groups, fossil fuels and biofuels, which are separated by where the carbon comes from and by how quickly the source is replaced. A resource is **renewable** when natural processes can replace it within a relatively short time, short enough to be set against the rate at which people use it. A resource that takes millions of years to form is treated as non-renewable, since it is used up far faster than it is made. ## Fossil fuels Fossil fuels formed from the remains of living things that were buried and changed by heat and pressure over millions of years. They are non-renewable. - Coal is mostly carbon, together with smaller amounts of hydrogen, oxygen, sulfur and nitrogen compounds, and is burned for heat and electricity. - Natural gas is mainly methane, $\ce{CH4}$, with smaller amounts of other light hydrocarbons such as ethane and propane. - Petrol is a liquid mixture of hydrocarbons, largely containing molecules of roughly five to twelve carbon atoms, obtained from crude oil by fractional distillation and further processing. Diesel and kerosene are heavier liquid fractions of the same kind. Burning any of them releases carbon dioxide that was locked away for a very long time, so the amount of carbon dioxide in the atmosphere rises. Sulfur in coal and…