Give reason why separation of mixtures example 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.
In the physical change, only the form of the substance is changed, and having same property. but no new product is formed.
On the other hand, when there is a chemical reaction, a completely different product is formed, whose properties are completely different from that of the reacting substances.
In your given example,
iron sulphur mixture have same property of iron and sulphur and the chemical composition of iron and sulfur remains the same.
But in case of heating of iron and sulphur, a new product iron sulphide is formed. This new product iron sulphide have completely differ property from iron and sulphur, hence it is a chemical change.