CombustionCombustion

D. Crowley, 2007D. Crowley, 2007

CombustionCombustion To be able to explain combustionTo be able to explain combustion

Wednesday, April 19, 2023Wednesday, April 19, 2023

Burning Natural GasBurning Natural Gas Look at the Look at the burning natural gasburning natural gas worksheet worksheet Answer the questions, using the diagram below for help…Answer the questions, using the diagram below for help…

Methane in low oxygen Methane 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

2CH4 + 3O2 2CO + 4H2O

CH4 + O2 C + 2H2O

CH4 + 2O2 CO2 + 2H2O

Burning Natural GasBurning Natural Gas CarbonCarbon ( (sootsoot) builds up in your chimney) builds up in your chimney The toxic gas The toxic gas carbon monoxidecarbon monoxide is produced is produced LessLess energy is released, as not enough oxygen reaches your energy is released, as not enough oxygen reaches your

burnerburner

Carbon monoxide can become deadly if you are subjected to Carbon monoxide can become deadly if you are subjected to high levels of it! Also, soot can cause respiratory problemshigh levels of it! Also, soot can cause respiratory problems

It will produce It will produce moremore energy and these waste substances, energy and these waste substances, carbon carbon dioxidedioxide and and waterwater

HeatingHeating Look at the demo of heating two beakers of waterLook at the demo of heating two beakers of water One is heated using the safety flame (yellow) and the other is One is heated using the safety flame (yellow) and the other is

heated using the fierce flame (blue)heated using the fierce flame (blue)

What difference is there?What difference is there?

CombustionCombustion Combustion is the chemical reaction which takes place when a Combustion is the chemical reaction which takes place when a

substance burnssubstance burns

The substance reacts with oxygen, releasing energy (heat and The substance reacts with oxygen, releasing energy (heat and light)light)

Combustion is extremely important (>90% of the world’s energy Combustion is extremely important (>90% of the world’s energy comes from combustion reactions (e.g. fossil fuels such as coal, comes from combustion reactions (e.g. fossil fuels such as coal, natural gas and petrol)natural gas and petrol)

What is needed for combustion to take place?What is needed for combustion to take place? HeatHeat FuelFuel OxygenOxygen

CombustionCombustion Combustion is Combustion is exothermicexothermic - heat is released to the surroundings - heat is released to the surroundings

This can also be called an This can also be called an oxidationoxidation reaction, as it involves oxygen reaction, as it involves oxygen being added to the fuelbeing added to the fuel

The fuel you use will result in different The fuel you use will result in different combustioncombustion reactions taking reactions taking place…place…

FuelFuel Coal is mostly Coal is mostly carboncarbon - when coal burns it turns limewater cloudy - when coal burns it turns limewater cloudy

(meaning the gas produced is carbon dioxide)(meaning the gas produced is carbon dioxide)

carbon + oxygen carbon + oxygen carbon dioxide carbon dioxide

Many other fuels are Many other fuels are hydrocarbonshydrocarbons - made up of hydrogen and - made up of hydrogen and carbon. When they burn they produce carbon dioxide and watercarbon. When they burn they produce carbon dioxide and water

methane + oxygen methane + oxygen carbon dioxide + water carbon dioxide + water

DemoDemo Watch the demo of complete combustionWatch the demo of complete combustion

Methane is our fuel: -Methane is our fuel: -

methane + oxygen methane + oxygen carbon dioxide + water carbon dioxide + water

CHCH4 + 2O + 2O2 CO CO2 + 2H + 2H2OO

What is the test for carbon dioxide produced?What is the test for carbon dioxide produced?

What is the test for the water produced?What is the test for the water produced?

Not Always PerfectNot Always Perfect A good supply of oxygen is needed for a fuel to burn completely and A good supply of oxygen is needed for a fuel to burn completely and

release as much energy as possiblerelease as much energy as possible

If there is a plentiful supply of oxygen we get If there is a plentiful supply of oxygen we get complete combustioncomplete combustion

However, if there is not enough oxygen then the fuel will not burn However, if there is not enough oxygen then the fuel will not burn completely, wasting both the fuel and reducing the energy releasedcompletely, wasting both the fuel and reducing the energy released

If there is not enough oxygen we get If there is not enough oxygen we get incomplete combustionincomplete combustion

Complete combustion

carbon + oxygen carbon dioxide

Incomplete combustion

carbon + oxygen carbon monoxide