Question

Which of the following is a chemical change?
A. Melting of wax
B. Dissolving sugar in water
C. Beating aluminium to make aluminium foil
D. Burning of coal

Answer 1

Hint: Changes in energy are always followed by a chemical change or physical change. The changes that are temporary comes under physical change. The changes that are permanent comes under chemical change.

Complete step by step answer:
When a substance is said to undergo a physical change, then only the physical properties such as the shape, size, colour, state, or appearance of the substance undergoes a change. The chemical composition remains unchanged. Physical changes are temporary in nature, does not affect the internal structure of a substance, no new substances are formed. The physical changes are reversible and thus can obtain the substance back even after the change. A substance undergoes a chemical change when the chemical properties of a substance changes. As a result, there is either formation or breaking of bonds. The chemical change is permanent in nature, here Since the one or more new substances are formed. Heat, light, or electricity, can be emitted or absorbed as energy. A chemical change is irreversible. It cannot be changed by simple physical means.
Combustion is an example of chemical change. In the above question, except burning of coal all processes are physical.
Burning of coal is a chemical change as here, different products are formed when carbon is reacting with oxygen. This reaction is also irreversible in nature.

\[{\text{Carbon + Oxygen }} \to {\text{ Carbon dioxide + Heat}}\]

So, the correct answer is Option D.

Note: The six common types of chemical reactions are, synthesis, decomposition, single-displacement, double-displacement, combustion, and acid-base reactions.
Some examples of physical change are, dissolution of sugar in water, melting of ice, freezing of water, boiling of water, and melting of wax. Some examples of chemical change are burning of wood or paper, burning of camphor, souring of milk, burning of candles and digestion of food.