A chemical reaction is represented by a chemical equation which show the reactant and products. Reactants are written on left side of arrow while products are written on right side. The number of atoms are remain same however arrangement of atoms is different on both side.
For example:
Cu(s) + 2AgNO3(aq) → 2Ag + Cu(NO3)2
In this reaction Cu and AgNO3 are reactants while Ag and Cu(NO3)2 are products.The number of atoms are same on both side however arrangement of atoms is different.
