Ethan is observing chemical and physical properties of a substance. He heats a substance and observes that the substance turns from a brown solid to a black powder. He refers to several chemistry journals that claim this represents a chemical reaction. From his observation and research, he concludes that the substance goes through a chemical change when heated. How can Ethan best defend his conclusion?

A chemical reaction is defined as the reaction which leads to change in chemical composition of the reactants due to which there occurs formation of a new compound.

For example, when Ethan heats a substance and observes that the substance turns from a brown solid to a black powder then it means heating has lead to a chemical change in the brown solid because of which it has turned into a black powder.

Whereas if there occurs no change in chemical composition of the reactants then we can say that a physical change has occurred.

For example, change in shape, size, mass etc of a substance are all physical changes.

Hence, we can conclude that Ethan best defend his conclusion as a chemical change.