Chemistry

Choosing a Fuel

It is important to choose the right fuel for the right thing.

Fuels are used for cooking, transport and heat.

Heat is released when a fuel burns. This is usefull energy.

Lots of oxygen is needed for complete combustion.

Complete combustion of a hydrocarbon fuel produces carbon dioxide and water only.

Comparing Fuels

Coal and petrol are fuels with different characteristics which could be used in a power station and in a car engine.

When coal and petrol are compared, coal produces more pollution then petrol.

However, coal is not as dangerous to store as it does not catch fire so readily.

Coal is not able to turn into gas easily but is dirty and takes up a lot of storage space.

Burning hydrocarbon fuels produces energy.

Fuel + Oxygen ----- Carbon Dioxide + Water

Hydrocarbons

Most of the compounds in crude oil are hydrocarbons. This means that they only contail hydrogen and carbon atoms, joined together by chemical bonds.

There are different types of hydrocarbons but most of the ones in crude oil are alkene.

Oxidation

Oxidation is the gain of oxygen by a substance. For example, magnesium is oxidised when it reacts with oxygen to form magnesium oxide:

magnesium + oxygen → magnesium oxide

2Mg + O₂ → 2MgO

Reduction

Reduction is the loss of oxygen from a substance. For example, copper oxide can be reduced to form copper if it is reacted with hydrogen:

copper oxide + hydrogen → copper + water

CuO + H₂ → Cu + H₂O

Many ores contain metal oxides, therefore many metals can be extracted from their ores by reduction reactions. The method used to extract a given metal depends on how reactive it is.

Alloys

The properties of a metal are changed by including other elements, such as carbon. A mixture of two or more elements, where at least one element is a metal, is called an alloy. Alloys contain atoms of different sizes, which distort the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal.

Composition of the Eaeth's atmosphere

You need to know the proportions of the main gases in the atmosphere.

The Earth's atmosphere has remained much the same for the past 200 million years. The pie chart shows the proportions of the main gases in the atmosphere.

It is clear that the main gas is nitrogen. Oxygen - the gas that allows animals and plants to respire, and fuels to burn - is the next most abundant gas. These two gases are both elements and account for about 99% of the gases in the atmosphere. 

The remaining gases, such as carbon dioxide, water vapour and noble gases such as argon, are found in much smaller proportions.

Oxygen in the air

The percentage of oxygen in the air can be measured by passing a known volume of air over hot copper, and measuring the decrease in volume as the oxygen reacts with it. Here are the equations for this reaction:

copper + oxygen    →    copper oxide

2Cu + O₂    →    2CuO

Gas syringes are used to measure the volume of gas in the experiment. The starting volume of air is often 100cm³ to make the analysis of the results easy, but it could be any convenient volume. In this simulation, there is 100cm³ of air at the start.