Standard Grade Chemistry - Chemical Reactions

Topic 1 revision notes.

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Typical Chemical Reactions

In all chemical reactions new substances are formed.
A new substance often looks different from the original substance.
Chemical reactions unlike physical reactions are difficult to reverse.
Energy changes take place in lots of chemical reactions
Reactions which take energy in are endothermic. Reactions which give energy out are exothermic.

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Signs Of Chemical Reactions

Colour Change

Property Change

Energy Change

Percipitate

Gas given off

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Elements

Everything is made up from about 100 elements.
Elements cannot be broken down into any simpler substances.
There is a different symbol for each element. They are listed in a chart called the periodic table.

Some elements have been known for a long time, these tend to be unreactive elements which are found native(pure), however most elements are found combined with others in compounds. Many elements have everyday uses. eg copper is used for water pipes and electrical wires.

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Compounds

Compounds are formed when elements join together.
Compounds ending in -ide usually contain only two elements.
Compounds ending in -ite or -ate usually contain three elements one of which is oxygen, -ate compounds
contain more oxygen than -ite compounds.
To separate compounds into elements requires a chemical reaction.

Compounds that end in ide have two elements present.

Compounds that end in ite, ate have oxygen also present.

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Mixtures

Mixtures are formed when two or more substances are mingled without reacting, examples are air and crude oil.
Separating substances in a mixture does not involve a chemical reaction, example iron and sulphur can be separated using a magnet.

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Solutes, Solvents And Solutions

A solvent is a liquid in which a substance dissolves.
A solute is a substance that dissolves in a liquid.
A solution is a liquid with a substance dissolved in it.

A dilute solution is one which contains a little solute in a lot of solvent.
A concentrated solution is one which contains a lot of solute to a little solvent.
Water is the most commonly use solvent.
A saturated solution is one in which no more solute will dissolve at that temperature.
An insoluble substance does not dissolve in the solvent.

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Everyday Reactions

Chemical Reactions

  • Fuels Burning
  • Iron Rusting
  • Copper Corroding
  • Beer Fermenting
  • Sausages Frying

Physical Reactions

  • Ice to Water
  • Water Vapour (Rain)
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