Topic 5 Revision

1. Topic 5 Revision Fuels are substances that burn given out energy. The main fuels that we use are coal, oil and natural gas. These fuels react with oxygen in a combustion reaction. The burning of fuels is an exothermic reaction, meaning that energy is given out.

2. Topic 5 Revision Pure oxygen will relight a glowing splint. There is not enough oxygen in the air for this to happen. Air is made up of 78% nitrogen, 21% oxygen, the remaining 1% is made of all the other gases.

3. Topic 5 Revision Coal is made from dead animals and plants that have been covered by mud. Over millions of years these plants and animals were subjected to temperature and pressure changes forming coal. Oil and gas are formed in a similar way, but from sea plants and animals.

4. Topic 5 Revision Since coal, oil and gas were formed millions of years ago they are called fossil fuels. Since these fossil fuels take millions of years to form they are rapidly running out. Since these fuels are running out we say that they are a finite resource, ie, there is a limited supply of them.

5. Topic 5 Revision Digging coal out if the ground leaves large holes that scar the landscape. Moving fossil fuels around can cause problems for the environment.

6. Topic 5 Revision Crude oil is transported around the world in huge oil tankers. Unfortunately these oil tankers get into difficulties and shed their load of crude oil. When this happens wildlife is badly affected as can the livelihoods of those who live by the sea.

7. Topic 5 Revision Crude oil is a thick black liquid which is a mixture of many different compounds. Crude oil is a useless mixture of compounds until they are separated out. This is done by fractional distillation. The crude oil is heated up and groups of molecules, fractions, evaporate at different temperatures making them easy to separate.

8. Topic 5 Revision The different fractions are made up of hydrocarbon molecules of different chain length. These fractions have different uses, depending upon their flammability and viscosity. The smaller the molecules the more flammable they are, and the less viscous they are.

9. suction candle lime water ice Topic 5 Revision The molecules that make up crude oil are called hydrocarbons. Hydrocarbons are molecules made from carbon and hydrogen only. This apparatus is used to show the products formed when hydrocarbons burn.

10. Topic 5 Revision A clear liquid that boils at 100ºC and freezes at 0ºC collected in the test tube in the ice bath. This clear liquid is water. The lime water turned cloudy, showing that lime water was also produced. The products of burning hydrocarbons in plenty of air (oxygen) are water and carbon dioxide. C3H8 + O2_________> CO2 + H2O propane 5 4 3

11. Topic 5 Revision When the supply of air (oxygen) is limited a different oxide of carbon is formed, carbon monoxide. Carbon monoxide is poisonous in small quantities as it stops the blood carrying oxygen to the brain. It is a colourless odourless gas. All homes with gas appliances should have a carbon monoxide detector. C5H12 + O2_________> CO + H2O pentane 5½ 6 5

12. Topic 5 Revision Sulphur is often found in fossil fuels as an impurity. When sulphur burns it forms sulphur dioxide. This gas dissolves in rain water to form acid rain. Sulphur should be removed from fossil fuels before they are burned. If the sulphur is not removed before burning the fossil fuel, the exhaust gases should be bubbled thought water to remove the sulphur dioxide.

13. Topic 5 Revision Normally oxygen and nitrogen from the air do not react together. However, in a car engine the spark from the spark plug has a high enough energy to make them react. When they do react nitrogen oxides are formed. These oxides are poisonous and also causes acid rain.

14. Topic 5 Revision Car engines produce both nitrogen oxides and carbon monoxide, both poisonous gases. To prevent these gases getting into the atmosphere they are passed over a catalytic converter. The catalytic converter changes nitrogen oxides and carbon monoxide into harmless gases, carbon dioxide and nitrogen. The metals used in a catalytic converted are transition metals.

15. Topic 5 Revision Until the year 2000 lead compounds were added to petrol to make it burn better. As these lead compounds are poisonous and cause brain damage in children the government banned their use. Carbon compounds like benzene are added to petrol instead. However, these compounds are carcinogenic (they cause cancer).