Chemistry Revision

Question answers
1. The three fossil fuels are crude oil, coal and natural gas
2. Non-renewable means a fuel that cannot be replaced, renewed, or it takes millions of years to make more
3. Fractional distillation is the name of the process that is used to separate crude oil.
4. The forces between molecules are intermolecular forces
5. The seven fractions collected in the fractionating column are LPG, petrol, naphtha, paraffin, heating oil, fuel oils, bitumen
6. The bigger the molecule, the higher the boiling point
7. A hydrocarbon is a compound consisting of hydrogen and carbon only
8. Cracking is the process that converts large, useless alkanes into more useful ones.
9. The conditions for cracking are a catalyst and a high temperature
10. When a hydrocarbon is burned, the 2 products are water and carbon dioxide
11. If a fuel releases 100KJ of energy when 5g is burned, the amount of energy released is 20KJ
12. When any hydrocarbon is burned in limited oxygen, the two products formed are water and carbon monoxide.
13. The oxide responsible for causing these things are as follows: a) smog = nitrogen dioxide. b) acid rain = sulfer dioxide. c) global warming = carbon dioxide.
14. The hydrocarbon that has single bonds are alkanes and the hydrocarbon that has double bonds is alkenes.
15. The chemical used to test for unsaturation is Bromine water; it goes from orange to colourless.
Topic 1
1. Crude oil is a mixture of hydrocarbons. These are separated into useful products, such as fuels, using a process called fractional distillation.
2. Alkanes are saturated - they have only single bonds. Alkenes have a double bond - they are unsaturated.
3. Alkanes are saturated hydrocarbons. This means their carbon atoms are joined to each other by single covalent bonds
4. Bromine water is a dilute solution of bromine that is normally orange-brown in colour, but becomes colourless when shaken with an alkene. Alkenes can decolourise bromine water, while alkanes cannot
5. Fuels made from oil mixtures containing large hydrocarbon molecules are not efficient. They do not flow easily and are difficult to ignite.
6. Smaller hydrocarbons are more useful as fuels, such as petrol.
7. alkenes are useful because they are used to make polymers
8. Fractions containing large hydrocarbon molecules are vaporised and passed over by a hot catalyst. This breaks chemical bonds in the molecules and forms smaller hydrocarbon molecules.
Topic 2
1. Fuels react with oxygen to release energy. Complete combustion happens in a plentiful supply of air and incomplete combustion occurs when the supply of air is limited.
2. Complete combustion releases more energy than incomplete combustion. Incomplete combustion also creates carbon monoxide, and more soot. Several factors must be considered when choosing the best fuel for a particular purpose.
3. The fossil fuels include coal, oil and natural gas. Various factors need to be considered when deciding how to use a fossil fuel. These include: the energy value of the fuel in kJ/g of fuel, the availability of the fuel, how the fuel can be stored, the cost of the fuel, the toxicity of the fuel - whether it is poisonous any pollution caused when the fuel is used, such as acid rain, how easy it is to use the fuel.
4. In general, solids such as coal are easier to store than liquids and gases but they are often more difficult to light. Liquids and gases ignite more easily. They also flow, which means they can be transported through pipelines.
5. Fuels are substances that react with oxygen to release useful energy. Most of the energy is released as heat, but light energy is also released. About 21 per cent of the air is oxygen. When a fuel burns in plenty of air, it receives enough oxygen for complete combustion
Topic 3
1. The Earth is surrounded by an atmosphere that is a mixture of gases. Some of these gases are molecular elements, and some are molecular compounds
2. The air contains a number of gases. The amount of water vapour in the air varies from place to place, and day to day. For this reason, the proportions of the gases in the air are usually given for dry air.
3. photosynthesis by plants is thought to be a key process in the evolution of the earths atmosphere
4. the atmosphere consists of mainly nitrogen and oxygen, with smaller proportions of other gases such as carbon dioxide.
5. the amount of carbon dioxide in the atmosphere is maintained through a balance between processes such as photosynthesis, respiration and combustion.

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