The rules, advantages and limitations for chemical equations are given in detail as follows.
Rules for writing chemical equations :
In writing a chemical equation representing a chemical reaction, certain rules have to be followed.
(i) The reactants taking part in the reaction are written in terms of their molecular formulae on the left-hand side of the equation.
(ii) A sign of plus (+) is added in between the formulae of the reactants.
(iii) The products of reaction are written in terms of their molecular formulae on the right-hand side of the equation,
(iv) A sign of plus (+) is added in between the products.
(v) In between the reactants and the products a sign of arrow(→)given to show which way the reaction is occurring.
Advantages of using a chemical equation :
(i) The representation of a chemical reaction becomes easy. It saves time and space in writing.
(ii) In order to prepare a definite amount of the product, the amount of the reactant to be used can be calculated accurately.
(iii) From a completely balanced chemical equation it becomes easy to determine the effect of temperature, pressure and concentration on the state of a reaction.
(iv) The meaning of a chemical equation is taken to be the same by chemists of any country of the world. Difference in language does not interfere with the meaning of the equation.
Limitations of chemical equations
1. A chemical equation does not indicate the physical stale of reactants and the products, i.e., it does not tell whether the substance involved in the reaction are solids, liquids or gases,
2. It does not indicate whether heat is evolved or absorbed as a result of reaction, i.e., it does not tell whether the reaction is exothermic or endothermic.
3. It does not indicate the conditions of reaction, i.e., it gives no idea about the pressure, temperature, concentration, presence of catalyst, etc. under which the reaction may occur,
4. It does not indicate whether the reaction is fast or slow.
5. Some reactions occur with explosion. This is not indicated by the chemical equation.
6. It does not tell about the actual amount of the reactants consumed or products formed. It gives only ratio.