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FORMULAE AND EQUATIONS
CONTENTS:
- Chemical formulae
- Chemical equations
- Empirical and Molecular formulae
- Relative Molecular Mass and Percentage composition by mass of an element.
PERIOD 1: CHEMICAL FORMULAE
Chemical formula can be defined as a collection of two or more symbols to represent one molecule of the compound. For example, the formula of tetraoxosulphate(VI) acid is H2SO4. This formula shows that in a molecule of tetraoxosulphate(VI) acid, there are two atoms of hydrogen, one atom of sulphur and four atoms of oxygen.
The table below contain examples of compounds with their formulae
| Compounds | Formulae |
| Oxygen molecule | O2 |
| Hydrogen molecule | H2 |
| Hydrogen chloride | HCl |
| Potassium chloride | KCl |
| Magnesium tetraoxosulphate(VI) | MgSO4 |
| Hydrogen sulphide | H2S |
| Bromine Molecule | Br2 |
| Ozone | O3 |
EVALUATION
Write the chemical formulae of the following:
(1) Sodium oxide, Calcium oxide, aluminium oxide,
(2) Carbon (IV) oxide, iron (II) oxide, copper(I) oxide
(3) Sodium tetraoxosulphate(VI), Calcium trioxonitrate(V), magnesium trioxocarbonate(IV).
PERIOD 2: CHEMICAL EQUATIONS
Chemical reactions are represented in form of equations which show the reactants and products in any given chemical reaction. For example, the reaction of aqueous hydrogen chloride and aqueous sodium hydroxide is represented by the equation:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Balancing Chemical Equations
All chemical equations must be balanced in order to comply with the law of conservation of mass. For example, to balance the equation for the reaction involving the combustion of ammonia gas in air, the following steps should be followed:
Step 1: The reactants (LHS) are NH3 and O2, while the products (RHS) are NO and H2O
NH3(g) + O2(g) → NO(g) + H2O(g)
Step 2: Place a 4 in front of NH3 and a 6 in front of H2O. There are now 12 hydrogen atoms on both sides of the equation.
4NH3(g) + O2(g) → NO(g) + 6H2O(g)
Step 3: Place a 4 in front of NO to balance with the 4 nitrogen atoms of the LHS of the equation.
4NH3(g) + O2(g) → 4NO(g) + 6H2O(g)
Step 4: Place a 5 in front of O2. An “atom count” shows that the equation is balanced.
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
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