Question

Give an example which shows both physical and chemical changes

Answer 1

A change can't be both physical and chemical, but physical and chemical changes can occur simultaneously. This is what's happening with the burning candle: the wax is melting, which is a physical change, and it's combusting, which is a chemical change. A physical change is a change in state, such as melting, freezing, evaporation or condensation, or a change in form, such as grinding a substance into a powder. There's no change in the chemical formula of the substance. A chemical change is one in which a new substance is formed.

The cycle of an internal combustion engine involves both a physical and chemical change. Gasoline is vaporized and the air in the cylinders is compressed, a physical change, before being ignited and combusting, a chemical change.

Digestion is another example of both. Food is physically broken down by chewing and chemically broken down by digestive enzymes in the saliva and acid in the stomach.

A third example is weathering in nature. Rocks are physically changed by wind, running water, expansion of ice as it freezes, abrasive wind and water-borne sediments. They are chemically changed by oxygen, acid rain and acidic compounds produced by decomposers.