Explanation:
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.
