Presentation on theme: "Combustion D. Crowley, 2007. Combustion To be able to explain combustion Saturday, August 15, 2015Saturday, August 15, 2015Saturday, August 15, 2015Saturday,"— Presentation transcript:
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