Rates of Reaction

Energy - Examples of Endothermic and Exothermic Reactions.

Most reactions are exothermic. Examples are

1) Combustion of methane (natural gas).

2) Neutralisation.

3) Adding concentrated sulfuric acid to water is
highly exothermic (gives out a lot of heat).

4) Adding water to anhydrous copper(II) sulfate is exothermic.
Anhydrous copper(II) sulfate is white.
Anhydrous is pronounced "an-high-drus"
Anhydrous means "without water".

Anhydrous copper(II) sulfate is copper(II) sulfate which is
completely dry. When water is added to it, it turns into the
familiar hydrated blue crystals.
Hydrated is pronounced "high-dray-tid", it means 'with water'.
This is used as a test for water.

If blue (hydrated) copper(II) sulfate crystals are heated,
an endothermic reaction occurs, they lose their water,
turn white and become
anhydrous copper(II) sulfate crystals again.
The reaction is reversible.
Blue copper(II) sulfate crystals will also turn white
in the presence of concentrated sulfuric acid.

Exothermic reactions can be
used to make hand warmers and self-heating cans.

Few reactions are endothermic. Examples are

1) Photosynthesis.
Chlorophyll is a very clever catalyst,
which allows plants to make sugar from carbon dioxide in the air.
The energy needed for the reaction comes from sunlight.

2) Thermal Decomposition.

3) The reaction of ethanoic acid with sodium carbonate.

4) Dissolving some salts in water is an endothermic process.
Potassium chloride and ammonium nitrate
both take in energy when they dissolve. If you put
a thermometer in the solution as they are dissolving,
you will see that the temperature drops.

5) Melting, boiling and evaporation
are all endothermic processes (not reactions).

Endothermic reactions can be used for injury packs in sports.

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