GCSE Revision Notes, Resources      

GCSE Chemistry > Chemical Changes

Thermal Decomposition
A single substance is broken down by heating. A good example of this is the cracking of hydrocarbons.

When one more reactive element pushes another less reactive element out of a compound. This mainly occurs with metals.

    e.g.   Magnesium   +   Iron Sulphate   ---->   Magnesium Sulphate   +   Iron

An acid and an alkali react to form a neutral product

A solid (the precipitate) is formed from the reaction of two solutions (i.e. no solids present at beginning of reaction)

Exothermic Reactions
A reaction that GIVES OUT heat. (e.g. combustion of fuels)

Endothermic Reactions
A reaction that TAKES IN heat. This energy is used to form the bonds needed to gain the products.

The GAIN of electrons. This is the opposite to oxidation.

    e.g.   Iron oxide   ---->   Iron

The LOSS of electrons. This is the opposite to reduction.

    e.g.   Iron   +   Oxygen   ---->   Iron Oxide

Reversible Reactions
When the reaction goes "both ways". The conditions surrounding the reaction determines which way the reaction favours i.e. more products or more reactants formed. (e.g. The Haber Process in forming ammonia)

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