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Rates of Reaction

Examples and Uses of Endothermic and Exothermic Reactions.

Most chemical reactions are exothermic.
Some examples are listed below.

1) The combustion of methane (natural gas)
is highly exothermic (it gives out a lot of heat).

2) Most neutralisation reactions are exothermic.

3) Adding concentrated sulfuric acid
to water is highly exothermic.

4) Adding water to anhydrous copper(II) sulfate is exothermic.

Anhydrous is pronounced "an-high-drus", it
means "without water". Anhydrous copper(II) sulfate
is copper(II) sulfate that is completely dry.
Anhydrous copper(II) sulfate is a white powder.

When water is added to the white powder it turns into
the familiar hydrated blue crystals. Hydrated is pronounced
"high-dray-tid", it means 'with water'. This
colour change from white to blue is used as a test for water.

If blue copper(II) sulfate is heated, an endothermic
reaction occurs and the blue crystals lose their water.
The crystals 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.

What are the Uses of Exothermic Reactions?

The combustion of methane is used for both
central heating in houses and to
generate electricity.
Other exothermic reactions can be
used to make hand warmers and self-heating cans.

Few chemical reactions are endothermic.
Some examples are listed below.

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

2) Thermal decomposition is endothermic.

3) The neutralisation reaction between
ethanoic acid and sodium carbonate is endothermic.

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 decreases.

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

What are the Uses of Endothermic Reactions?

Endothermic reactions can be used for injury packs in sports.

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