Mixing iron filings with sulphur is considered to be a physical change because the mixture can be easily separated and no new substance is formed .
Moreover, no energy change occur while mixing iron and sulphur.
When the mixture is heated , the two substance combine to form a new substance known as ferrous sulphide .
The original substances iron and sulphur cannot be re_obtained by cooling ferrous sulphide . consequently, it is a permanent chemical change involving a energy change.