It is generally termed as when a substance came into contact with another substance and then another substance is produced. Chemical change is accompanied by series of evidence that can be noticed in a system. Some of its apparent evidences are change of the state of the matter, production/release of a gas, new odor, formation of precipitate, change in colour, disappearance of substance, increase in temperature and violent/explosive reaction.
In this connection, single evidence may or may not be sufficient.
1. Temperature increase shows that there has been a chemical change.
2. Ice melts at temperature higher than 0 degrees Celsius. Melting and freezing are physical changes.
3. Two things happen in the crucible: Disappearance of the reactants, formation of new substance after heating.