Fuels and their elements
Assignment 14.1 asks you to list some fuels used in everyday life and find out which elements they contain.
Assignment 14.1
List several kinds of fuel used in everyday life. Find out about the chemical composition (the elements contained) of those fuels. Compare your list with table 14.1.
| Fuel | Elements it contains |
|---|---|
| Candle wax | C, H |
| Petrol | C, H |
| Methane | C, H |
| LP gas | C, H |
| Kerosene | C, H |
| Diesel | C, H |
| Firewood | C, H, O, N |
Every fuel in the table contains carbon (C) and hydrogen (H). Firewood contains oxygen and nitrogen as well, because wood is made of the compounds of a living plant, such as cellulose.
Why fuels are made of carbon and hydrogen
A fuel is useful because burning it gives out a lot of heat. When a hydrocarbon burns, its carbon joins with oxygen to make carbon dioxide and its hydrogen joins with oxygen to make water, and both reactions are strongly exothermic — the heat changes of chapter 8. So a compound built almost entirely of carbon and hydrogen is exactly what makes a good fuel. Wood already has some oxygen locked into it, so it has less to gain from burning, and it gives out less heat for its weight than petrol or gas.
Hydrocarbon means only C and H
Firewood contains carbon and hydrogen but also oxygen and nitrogen, so it is not a hydrocarbon. The fuels from petroleum are.
Fuels contain carbon and hydrogen
Candle wax, petrol, methane, LP gas, kerosene and diesel all contain only C and H; firewood contains C, H, O and N.