The symbolic representation of chemical reaction is called a chemical equation.
Characteristics:
A chemical equation conveys many informations as described below:
1. It tells about the names of the reactants and products of a chemical reaction.
2. It expresses the number of molecules of reactants and products.
3. It expresses the relative weights of the reactants and the products.
4. It expresses the volumes of the gaseous reactants and products.
Example:
Ammonia gas is formed by the combination of nitrogen and hydrogen, its chemical equation representing the reaction is:
N2 + 3H2→ 2NH3
(14 x 2) + 3 (1 x 2) = 2(14 +1×3)
The above equation expresses that:
1. Nitrogen combines with hydrogen to form ammonia.
2. One molecule of nitrogen combines with three molecules of hydrogen to form two molecules of ammonia.
3. 28 parts by weight of nitrogen have combined with 6 parts by weight of hydrogen to form 34 parts by weight of ammonia.
4. One volume of nitrogen and three volumes of hydrogen combine together to give two volumes of ammonia.
Limitations of a chemical equation:
1. A chemical equation does not always give an idea about the physical state of the reactants and products, whether these are solid, liquid or gas.
2. A chemical equation does not always indicate the conditions necessary for the reaction (i.e. temperature, pressure, the presence of a catalyst).
3. It does not give any idea about the rate of the reaction, whether it is slow or fast.
4. An equation fails to give any indication whether heat is evolved or absorbed.
5. It does not give any idea about the concentration of the reactants.
6. It fails to give any idea about the j mechanism of the reaction.
7. The above equation does not give any indication about the nature of the reaction, whether it is reversible or irreversible.