Chemistry Unit 2

Unit2.5: Hydrocarbons

Fossil fuels – is one that derived from organisms long ago

Use of fossil fuels

·         They are available in a variety of forms so the type of fuel can be matched to its use (e.g. gas is used in power stations)

·         They are available at all times

·         They are non – renewable

·         Combustion of fuels produces carbon dioxide this is a greenhouse gas

Greenhouse gas – is one that causes an increase in the Earth`s temperature by absorbing the IR from the Sun and re-mitting it in all directions

Acid rain – many fossil fuels contain sulphur which dissolve in water to make sulphuric acid. This can cause serious damage to buildings, especially if they contain calcium carbonate. It is also a problem for people with breathing difficulties

Carbon monoxide formation – if fossil fuels are burnt in an inadequate supply of oxygen, carbon monoxide can be formed. This irreversibly combines with haemoglobin, making it unable to carry oxygen. This can cause death.

Alkanes

Since the electronegativity of carbon and hydrogen are similar, they are non – polar and have no multiple bonds they are generally unreactive. The C-C and C-H bonds are sigma bonds in alkanes.

They can react in combustion reactions and halogenation reactions

1.       Combustion – alkanes burn by reaction with oxygen in an exothermic reaction (If sufficient oxygen water is present, complete combustion occurs and carbon dioxide and water are formed. If insufficient oxygen is present, carbon monoxide and water are formed

2.       Halogenation – this is the reaction between an organic compound and any halogen. Initiation starts the reaction when UV light is present because it has the right energy to break the bonds. Homolytic bond fission occurs, each of the bond atoms receives a bond electron so that radicals are formed. Radicals are reactive and take place in a series of…