A change that does not alter the chemical composition of a substance is called?

A change that does not alter the chemical composition of a substance is referred to as a physical change. This type of change involves transformations that affect the form or appearance of a substance but leave its chemical structure intact. For example, when water freezes into ice or melts back into liquid, the H₂O molecules remain unchanged, just in different physical states.

In contrast, a chemical change would involve a transformation that alters the substance's chemical structure, such as when wood burns and turns into ash and gases. A nuclear change involves alterations to the nucleus of an atom, resulting in the transformation of one element into another, which is quite distinct from changes we observe in everyday physical states. Isotopic change refers to variations in the number of neutrons in the nucleus, leading to different isotopes of an element, but again does not fit the definition of a change where the substance's chemical identity remains the same.