Which of the following is a physical change ?
a) Melting of butter b) Burning of paper c) Rusting of iron d) Changing of wheat into bread
The correct answer and explanation is:
The correct answer is a) Melting of butter.
A physical change is a change in a substance that does not alter its chemical structure. The substance undergoes a transformation in its physical properties, such as shape, size, or phase, but its chemical composition remains unchanged.
In the case of melting butter, the process involves the conversion of butter from a solid to a liquid state when heat is applied. This change is purely physical because the molecular structure of butter remains intact. It’s simply the arrangement of molecules that shifts due to the increase in temperature. The chemical composition of butter, made up of fats and water, does not change in any way during the melting process. If the butter is later cooled, it will solidify again without any chemical reaction, further confirming that this is a physical change.
On the other hand, the other options involve chemical changes:
- Burning of paper: This is a chemical change because the paper undergoes combustion, a chemical reaction with oxygen, resulting in the formation of new substances like carbon dioxide, ash, and water vapor.
- Rusting of iron: Rusting is a chemical change as iron reacts with oxygen and water to form iron oxide, a completely new substance.
- Changing wheat into bread: This involves both chemical and physical changes. The wheat undergoes a series of chemical reactions during baking, such as the Maillard reaction and fermentation, which produce new compounds that make bread distinct from its original ingredients.
In summary, the melting of butter is a physical change because it only involves a change in the physical state of the substance, not its chemical composition.