Many things around us keep changing – milk turns into curd, vegetables decay and iron turns reddish brown. Some of these are physical changes and some are chemical changes. Yet the rust resistant iron pillar at Qutub Minar in Delhi has not rusted for more than 1500 years. This chapter explains what a chemical change is, the factors that determine chemical changes and the effects of chemical changes.
1. Physical and Chemical Changes
A chemical change is a permanent and irreversible change which produces a new substance. Chemical changes are also called chemical reactions, because one or more substances (reactants) undergo a reaction to form one or more new substances (products).
Reactant(s) → Product(s)
| Physical Changes (examples) | Chemical Changes (examples) |
|---|---|
| Folding and unfolding a paper | Burning of paper |
| Drying wet clothes | Digestion of food |
| Bending of iron rod | Turning of milk into curd |
| – | Decaying of vegetables |