Question

Define chemical change with an example.

Answer 1

1. Definition: A change in which the composition of a substance is altered is called a chemical change.
2. The original properties get changed and one or more new substances are formed.
3. This means that chemical changes are irreversible.
4. The components of a new substance formed cannot be separated by physical methods.
5. It includes burning of candle wax, burning of paper, ripening of fruits, growth of a plant, digestion of food, rusting of iron, formation of curd from milk burning of fuels, etc.

Example:

• Burning of Paper: When a sheet of paper is burnt, new substances like carbon dioxide, water vapour, smoke, and ash are produced.
• Heating of Magnesium Wire: When Magnesium$\left(\mathrm{Mg}\right)$ wire is heated, it burns to form a new substance, a white powder of Magnesium oxide$\left(\mathrm{MgO}\right)$.