Definition and explaining of chemical equation

The method of representing a chemical reaction with the help of symbols and formulae of substances involved in it is called a chemical equation.

Example: Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.

This equation is written as: Zn + H₂SO₄ →ZnSO₄ + H₂

• Writing Chemical Equations:

1. In  a  chemical  reaction,  the  reactants  are  written  on the  left  hand  side  and  the  products  on  the  right hand side of the equation.
2. An arrow (→) pointing towards the products is inserted between the reactants and the products. It also represents the direction of the reaction.
3. A single arrow (→) indicates the direction in which the reaction proceeds.
4. A double arrow (⥮) indicates a reversible reaction, i.e. the products recombine to form the reactants.
5. A plus sign (+) is inserted between two or more reactants or products formed.
6. If reactions are carried out under specific conditions of temperature, pressure, catalyst etc., then these conditions are mentioned on the arrow.

The  chemical  equation  can  be  made  more  informative  by  mentioning  the  physical  states  of  the reactants and products.

1. If gas is liberated as a product then it is represented by an arrow pointing upwards (↑).
2. If the product formed is in the form of a precipitate, it is represented by an arrow pointing downwards (↓).