Changes around us · हमारे आस-पास के परिवर्तन
A free Chemistry lesson for Class 6 children.
Some changes can be undone. Ice melting into water can be reversed by freezing. These are reversible changes.
Some changes cannot be undone. A burnt paper or a cooked chapati cannot go back. These are irreversible changes.
Heating makes metals expand a little. A blacksmith heats an iron rim so it fits over a wooden wheel, then cools it to shrink it tight.
Dissolving salt in water is reversible: evaporate the water and the salt is back.
Mixing cement with water and letting it set is irreversible.