A chemical reaction is represented by a 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
- An equation should be written with reactants at the left-hand side and products at the right-hand side
- The correct formula for each substance is written underneath
- The number of atoms of each elements involved are counted on both sides to see if they are equal
- Numbers are written in front of formula until the number of atoms are balanced
Balancing chemical equations
- 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
- Heating copper(ii)carbonate
HEAT
CuCO3 CuO + CO2
Copper(ii)carbonate copper(ii)oxide + carbon dioxide
- Heating of sugar
HEAT
C6H12O6 6C + 6H2O
SUGAR carbon + water
- Burning phosphorus in oxygen
HEAT
P4 + O2 2P2O
- Burning of magnesium
HEAT
2Mg + O2 2MgO
- 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
A white precipitate is observed as soon as the two liquids are mixed hence a salt called sodium chloride.
- 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)