What are the chemical reactions?

A chemical reaction happens when one or more chemicals (Reactants) are changed into one or more other chemicals (Products). 

Examples: iron and oxygen combining to make rust.

Vinegar and baking soda combining to make sodium acetate, carbon dioxide and water.

Balanced Chemical Equation: A balanced chemical equation has number atoms of each element equal on both left and right sides of the reaction.

In order to balance chemical equations, one has to balance all the atoms on the left and right side of the arrow.

for example: Mg + H₂SO₄ --> MgSO₄ + H₂

 left side : Mg = 1          right side of arrow: Mg = 1

     

             H = 2                                  H = 2

    

             S = 1                                 S = 1

     

              O = 4                                  O = 4

As you can see that the elements on both left and right side have equal no. of atoms, therefore the equation is balanced.