State four conditions necessary for chemical reactions to take place.

The four conditions necessary for chemical reactions to take place are:

1. Close contact: For a chemical reaction to take place the reactants must come into close contact i.e. they should be mixed.
2. Solution form: Some substances react with each other only when they are mixed in solution form.
3. Heat: Some reactants need to be heated to undergo a chemical change.
4. Light: Some reactions take place in the presence of light.