There are nine basic types of chemical change-

Thermal decomposition

This isn't a reaction because there is only one substance involved. The substance is heated and breaks down into simpler substances. The cracking of hydrocarbons is a good example of this.

Exothermic


Any reaction that gives off heat is exothermic. A fuel burning is an exothermic reaction.

Endothermic


An endothermic reaction requires heat to make it work. This heat is used to form chemical bonds. Extracting iron from haematite is an endothermic reaction - it needs a lot of heat from the coke to keep it happening.

Neutralization


A neutralisation reaction involves an acid and an alkali reacting together to give a neutral solution (often a salt), along with water.

Displacement


A displacement reaction involves one element which is more reactive than another element displacing it and taking its position. For instance, Magnesium + Iron Sulphate -> Magnesium Sulphate + Iron.

Precipitation


This is a reaction where two solutions react, forming a solid that sinks to the bottom. This solid is said to "precipitate out".

Oxidation


Oxidation is the loss of electrons, by the addition of oxygen. For instance, iron becoming iron oxide is oxidation.

Reduction


The opposite of oxidation, this involves the loss of oxygen and the gain of electrons. Iron oxide is reduced to iron.

Reversible reactions


These reactions can quite easily both go ways - i.e. the products can easily be changed back into the original reactants.

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