• Chemical reactions

A chemical reaction is represented by a chemical equation.

• Chemical equation

It’s a representation of a chemical change by means of symbols and formulae. It gives a detail explanation of the elements and compounds in a chemical reaction to a chemist.

Reactants and products

Reactants are elements or compounds that take part in a chemical reaction to form a new compound called Products.

Rules in writing and balancing chemical equations

1. An equation should be written with reactants at the left-hand side and products at the right-hand side
2. The correct formula for each substance is written underneath
3. The number of atoms of each elements involved are counted on both sides to see if they are equal
4. Numbers are written in front of formula until the number of atoms are balanced

Balancing chemical equations

1. In the decomposition of hydrated copper(ii)sulphate

Decomposition is the breakdown of molecules or substances by the use of heat.

Hydrated means it contains water of crystallization.

                       HEAT

CuSO4.H2O                        CuSO4 + H2O

N.B: CuSO4.H2O= hydrated copper(ii)sulphate(blue colour)

CuSO4=copper sulphate

H2O=water

2. Heating copper(ii)carbonate

                  HEAT         

CuCO3                          CuO + CO2

Copper(ii)carbonate         copper(ii)oxide + carbon dioxide

3. Heating of sugar

                      HEAT

C6H12O6                          6C + 6H2O

SUGAR                                   carbon + water

4. Burning phosphorus in oxygen

                   HEAT

P4 + O2                        2P2O

5. Burning of magnesium

                        HEAT

2Mg + O2                          2MgO

6. Reaction with some metals

Ca + 2H2O                         Ca(OH)2 + H2

THE LAW OF CONSERVATION OF MASS

Matter is neither created no destroyed in a chemical reaction. This means that in all reactions, mass of reactants is always equal to the mass of the products.

An experiment to prove the above law

• Aim: to illustrate the conservation of mass by reacting hydrochloric acid with sodium hydroxide solution
• Requirements: glass beaker, sodium hydroxide solution ,hydrochloric acid solution, test tubes ,bromothymol blue, weighing chemical balance
• Procedure:

• weigh a clean, dry glass beaker on a chemical balance
• pour 20ml sodium hydroxide solution into a beaker
• add a few drops of bromothymol blue solution to the contents of the beaker and record the colour
• add 20ml o hydrochloric acid solution to the contents of the beaker. If there is no colour change, add a few more drops of hydrochloric acid solution. Record the colour change, the final colour must be green.
• Record the final mass of the beaker

• Observation:

A white precipitate is observed as soon as the two liquids are mixed hence a salt called sodium chloride.

• Conclusions:

• The white precipitate shows the formation of a new substance as a result of the chemical reaction
• The weight of the new substance formed is equal to the original weigt taken before the reaction.
• This therefore means that there is no change of mass as the sodium hydroxide solution reacts with the hydrochloric acid solution.

NaOH(aq) + HCl (aq                             NaCl(aq) + H2O(l)