Combustion of hydrocarbon fuels
Most fuelMaterial that is used to produce heat, like coal, oil or gas. contain carbon and/or hydrogen. When hydrogen atomAll elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. are present in a fuel, they are oxidationThe gain of oxygen, or loss of electrons, by a substance during a chemical reaction. to water. Water is not a pollutantA toxic chemical or object that causes damage to the land, air or water..
When there are lots of oxygen atoms present during combustionThe process of burning by heat., the carbon atoms are completely oxidised to carbon dioxide. When there are fewer oxygen atoms present, carbon monoxide or carbon may be produced during combustion.
Complete combustion
complete combustionBurning in a plentiful supply of oxygen or air. Complete combustion of a hydrocarbon produces water vapour and carbon dioxide. of a hydrocarbonA compound that contains hydrogen and carbon only. fuel occurs when there is a good supply of oxygen. It releases the maximum amount of energyThe capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. and produces carbon dioxide and water.
To construct a symbol equation for the complete combustion of a hydrocarbon fuel, remember that the fuel reacts with O2 and the only products are CO2 and H2O. For example, using methane (CH4) as the fuel:
methane + oxygen → carbon dioxide + water
CH4 + O2 → CO2 + H2O
When this equation is balanced, you get:
CH4 + 2O2 → CO2 + 2H2O
Incomplete combustion
incomplete combustionBurning when there is a limited supply of air or oxygen. of a hydrocarbon fuel occurs when there is a poor supply of oxygen. Less energy is released. Water is still produced from the hydrogen atoms. Instead of carbon dioxide, you might get carbon monoxidePoisonous gas produced during incomplete combustion. or sootThe fine black particles, chiefly composed of carbon, produced by incomplete combustion of coal, oil, wood, or other fuels., known commonly as soot, or a mixture of both.
To construct a symbol equation for the incomplete combustion of a fuel, you need to read the question to see whether carbon monoxide (CO) or carbon (C) is produced. For example, using ethane (C2H6) as a fuel, and producing CO as one of the products:
ethane + oxygen → carbon monoxide + water
C2H6 + O2 → CO + H2O
When this equation is balanced, you get:
2C2H6 + 5O2 → 4CO + 6H2O
Problems with incomplete combustion
Carbon monoxide is a poisonous gas which binds to haemoglobinThe red protein found in red blood cells that transports oxygen round the body. in your red blood cells, preventing them from carrying oxygen to the cells in your body. Carbon monoxide is colourless and has no smell, so it is very difficult to tell if you are breathing it in. It can be detected by electronic detectors which are often fitted near to boilers.
Particulate carbon can cause health problems for humans because it irritates the lining of the lungs, can make asthmaA disease that affects the respiratory system. worse, and perhaps even cause cancerA disease caused by normal cells changing so that they grow and divide in an uncontrolled way. The uncontrolled growth causes a lump called a tumour to form.. Particulate carbon can also cause global dimmingThe gradual reduction in radiation energy which reaches the Earth's surface from the Sun due to small particles in the atmosphere which have almost certainly been produced by human activities such as burning fossil fuels., which may reduce rainfall.