What Is Chemical Equation?

We will first try to understand the basic difference between Chemical Reaction and Chemical Equation.

Chemical Reaction

The reaction in which a chemical substance transforms into another chemical substance is known as a chemical reaction. In this type of reaction a completely new substance is formed which is different from the original substance and it involves a chemical change. A chemical change involves formation of new substances whereas a physical change involves a change in color or state and no new substances are formed. During a chemical reaction, the substances that react are known as reactants whereas the substances that are formed during a chemical reaction are known as products. Following are the signs that show that chemical reaction is taking place:

  • Evolution of gas
  • Evolution of light and sound
  • Formation of a precipitate
Chemical Equation


Chemical Equation

The representation of a chemical reaction in the form of symbols (substances) is known as a chemical equation. A chemical equation is formed with the help of reactants, products and an arrow. The reactant molecules interact with each other such that new bonds are formed resulting in the formation of products. In the reaction shown below, A reacts with B to form the products X and Y. The arrow shows the direction of the reaction

A + B → X + Y

Symbols used for physical states of reactants and products: For solids we use‘s’, for liquid we use ‘l’ and for gas we use ‘g’. For an aqueous solution, we use ‘(aq)’.

Example: Zn + H2SO4 →   ZnSO4 + H2

The equation in which the number of atoms or molecules is equal on both sides of the equation is known as balanced chemical equation. In the equation given above, the number of zinc, hydrogen and sulphate are equal on both sides; therefore, it is an example of balanced chemical equation.

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Practise This Question

Write the following in the form of a word equation:
Sodium hydroxide reacts with calcium bromide to form calcium hydroxide and sodium bromide.In the formula CaBr2​ what does Ca stand for and what is its valency?