It is a chemical change.
As explained by MCWDN.org, a physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.
Physical changes can be reversed, chemical changes cannot be reversed with the substance changed back without extraordinary means, if at all. Once you cook a hamburger, you cannot uncook it and start off with fresh ground beef again.
When heat is given off in a chemical change or reaction, it is called an exothermic reaction. When heat is absorbed in a chemical change or reaction, it is called an endothermic reaction. The speed at which chemical reactions take place depend on the temperature pressure and how concentrated the substances involved in the chemical reaction are. Sometimes substances called catalysts are used to speed up or help along a chemical reaction.
Learn more about the difference between chemical and physical change at Antoine.
Find more Examples of Physical Changes and Chemical Changes at ThoughtCo.