Combustion D. Crowley, 2007

Combustion  To be able to explain combustion Saturday, August 15, 2015Saturday, August 15, 2015Saturday, August 15, 2015Saturday, August 15, 2015

Burning Natural Gas  Look at the burning natural gas worksheet  Answer the questions, using the diagram below for help… Methane in low oxygenMethane in high oxygen In low oxygen two chemical reactions take place: - In normal air (high oxygen) one chemical reactions takes place: - methane + oxygen  carbon monoxide + water methane + oxygen  carbon + water methane + oxygen  carbon dioxide + water 2CH 4 + 3O 2  2CO + 4H 2 O CH 4 + O 2  C + 2H 2 O CH 4 + 2O 2  CO 2 + 2H 2 O

Burning Natural Gas  Carbon (soot) builds up in your chimney  The toxic gas carbon monoxide is produced  Less energy is released, as not enough oxygen reaches your burner  Carbon monoxide can become deadly if you are subjected to high levels of it! Also, soot can cause respiratory problems  It will produce more energy and these waste substances, carbon dioxide and water

Heating  Look at the demo of heating two beakers of water  One is heated using the safety flame (yellow) and the other is heated using the fierce flame (blue)  What difference is there?

Combustion  Combustion is the chemical reaction which takes place when a substance burns  The substance reacts with oxygen, releasing energy (heat and light)  Combustion is extremely important (>90% of the world’s energy comes from combustion reactions (e.g. fossil fuels such as coal, natural gas and petrol)  What is needed for combustion to take place? Heat Heat Fuel Fuel Oxygen Oxygen

Combustion  Combustion is exothermic - heat is released to the surroundings  This can also be called an oxidation reaction, as it involves oxygen being added to the fuel  The fuel you use will result in different combustion reactions taking place…

Fuel  Coal is mostly carbon - when coal burns it turns limewater cloudy (meaning the gas produced is carbon dioxide) carbon + oxygen  carbon dioxide  Many other fuels are hydrocarbons - made up of hydrogen and carbon. When they burn they produce carbon dioxide and water methane + oxygen  carbon dioxide + water

Demo  Watch the demo of complete combustion  Methane is our fuel: - methane + oxygen  carbon dioxide + water CH + 2O  CO + 2HO CH 4 + 2O 2  CO 2 + 2H 2 O  What is the test for carbon dioxide produced?  What is the test for the water produced?

Not Always Perfect  A good supply of oxygen is needed for a fuel to burn completely and release as much energy as possible  If there is a plentiful supply of oxygen we get complete combustion  However, if there is not enough oxygen then the fuel will not burn completely, wasting both the fuel and reducing the energy released  If there is not enough oxygen we get incomplete combustion Complete combustion carbon + oxygen  carbon dioxide Incomplete combustion carbon + oxygen  carbon monoxide