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A chemical reaction ALWAYS forms a new substance.

Signs that show a chemical reaction has taken place are:

i. A change in colour
ii. A change in temperature (usually gets hot)

Types of reaction



Oxidation and reduction





Identifying Chemicals



Burning always produces an OXIDE.

Burning an element produces ONE oxide.

Burning a compound produces TWO or more oxides.

The mass of the oxides formed will always be MORE than the mass of the substance being burned. (why?)

eg i. Burning magnesium

Burns with bright white flame to form magnesium oxide

Word equation: Magnesium + oxygen ----> magnesium oxide

Burning Methane (natural gas)


It burns with a smoky flame to form carbon dioxide and water

Word equation: Methane + oxygen ------> carbon dioxide and water

Alcohol will also burn to form carbon dioxide and water.

2. Decomposition



Each new substance formed will have LESS mass than the original substance

eg i. Heating copper sulphate


Word equation: Hydrated copper sulphate ----> anhydrous copper sulphate + water



Word equation: Copper carbonate ----> copper oxide + carbon dioxide

iii. Heating limestone

The limestone decomposes and forms LIME and carbon dioxide gas

Word equation: Calcium carbonate -----> calcium oxide + carbon dioxide

or Limestone -----> lime + carbon dioxide

3. Oxidation and Reduction


Reduction is when a substance has oxygen taken away from it.

eg i. Heating carbon with copper oxide


Word equation: Carbon + copper oxide -----> carbon dioxide + copper


Placing burning magnesium in carbon dioxide

Word equation: magnesium + carbon dioxide -----> magnesium oxide + carbon

Reactions with acid : Neutralization

i. Adding dilute hydrochloric acid to marble


Word equation
Hydrochloric acid + calcium carbonate ------> calcium chloride + carbon dioxide

Adding dilute hydrochloric acid to dilute sodium hydroxide solution.


Word equation
Hydrochloric acid + sodium hydroxide ------> sodium chloride + water

Reactions in Biology

 i Respiration

Word equation: Glucose + oxygen ----> carbon dioxide + water

ii Photosynthesis


Word equation    Carbon dioxide + water -----------> glucose + oxygen 
(Chlorophyll+ sunlight)

iii Fermentation


Word equation: sugar ----> carbon dioxide + alcohol

How to identify chemicals:
(This shows that a liquid contains water)

Physical test: Measure the boiling point which should be100 C
(this shows that a liquid is pure water)

Hydrogen:  Hydrogen burns with a squeaky 'pop'.
Oxygen Oxygen will re-light a glowing splint.

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