Differentiate between physical and chemical changes. Give two examples of each, explaining why they are classified as such.
BiologyClass 9CBSEAnswered 12 May 2026
Answer
A physical change is a change in the form or appearance of a substance, but not in its chemical composition. No new substance is formed, and the change is often reversible. Examples:
- Melting of ice: Ice (solid water) changes to liquid water, but it's still H₂O. No new substance is formed.
- Dissolving sugar in water: Sugar molecules are dispersed in water, but their chemical identity remains the same.
A chemical change (or chemical reaction) results in the formation of new substances with different chemical properties. It is usually irreversible.
Examples:
- Burning of wood: Wood combines with oxygen to produce ash, carbon dioxide, and water vapor, all new substances.
- Rusting of iron: Iron reacts with oxygen and water to form iron oxide (rust), a new substance with different properties.
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