What are reversible and irreversible reactions? Give examples.

Reversible reactions: Reactions which proceed in both directions are called reversible reactions. In a reversible reaction, the reactants are changed into products and simultaneously the products are changed into reactants. A reversible reaction is shown by using two half arrows in opposite direction .  In a reversible reaction, the reaction proceeding from left to right (reactants that give the products) is called forward reaction. The reaction proceeding from right to left (products that give back the reactants) is called a backwards reaction. The reversible reaction generally proceeds in a closed vessel. This prevents the escape of the products. Example of reversible reaction are:

Irreversible reactions: A chemical reaction is said to be irreversible if reactants are changed into products (proceeds only in the forward direction) but the products do not combine to form the reactants. These reactions are indicated by a single arrow  in a chemical equation. Examples of irreversible reactions are:
 (i) Burning of magnesium
           
(ii) Decomposition of potassium chlorate. 
(iii) The reaction between hydrogen and oxygen to form water vapours.