'One way changes are classified is reversible and irreversible'. Explain with examples.

Consider the example, when salt is mixed with water. The salt dissolves in water forming a solution. The salt can be obtained back by the evaporation of water and water by condensation of the water vapour. Such changes which can be easily reversed are called reversible changes.

Consider the example of rusting of iron. When an iron is kept in humid air for some days, a brown substance (rust) deposits on it, which has very different properties from that of iron. There is no simple way to get back the iron from the rust. Such changes which cannot be reversed are called irreversible changes.