What is a chemical change?

Peace be upon you, Sir.

Your question is very vague. There is so many angles to answer this from. I hope you will supply more information.

I am assuming that you are asking about chemical reactions, with respect to chemical change.

Hence, from that angle solely, it is a change in the substance as it undergoes a chemical reaction to form another substance(s). It can be reversible or irreversible, pending the reaction kinetics of that particular reaction that the substance is subjected to.

Hope this helps.

Chemical Change is like your life every second you pass can never come back, in same way if we take chemical reaction example, once reactants are converted to products, they can not take previous shape, if it is possible to bring them with same properties then it is not a chemical change.

Chemical change is any modification or switching which evolves in the formation of new chemical species. At the molecular level, chemical change encompasses creation or rupturing of joins linking atoms. For eg: rusting of iron which leads to formation of oxide layers on its surface.