Question

Give reasons why – separation of mixtures e.g. iron from a mixture of iron and sulphur is a physical change, but heating a mixture of iron and sulphur is considered a chemical change.

Answer 1

Physical change

1. There is no change in the specific properties of the constituents.
   Example: The particles of iron can be separated from sulphur with the help of a magnet or by dissolving sulphur in carbon disulphide.
2. No new substance is formed.
   Example: The mixture of iron and sulphur does not form any new substance.
3. There is no net release or absorption of energy.
   Example: When iron and sulphur particles are mixed, heat energy is neither given out nor absorbed.
4. It is a temporary change and can be reversed by removing the cause of the change.
   Example: The particles of iron can be separated from the mixture with the help of a magnet. removing the cause of change.

Chemical change

1. There is a specific change in the properties of the constituents.
   Example: The particles of iron or sulphur cannot be separated by a magnet or carbon disulphide.
2. A new substance is formed.
   Example: Iron sulphide is the new substance formed when iron and sulphur are heated.
3. There is a net release or absorption of energy when a chemical change takes place.
   Example: When iron sulphide is formed, the test tube gets red hot on account of the release of a large amount of heat energy.
4. It is a permanent change and cannot be reversed by removing the cause of the change.
   Example: The particles of iron can be separated from the mixture with the help of a magnet. removing the cause of change.