What type of change occurs when a substance's identity remains the same?

A physical change occurs when a substance undergoes a transformation that does not alter its chemical identity. This means that despite the change in form, state, or appearance, the substance itself remains chemically the same. Common examples of physical changes include melting, freezing, boiling, and dissolving. These processes can typically be reversed, allowing the original substance to be recovered in its original state.

In contrast, a chemical change involves a transformation that changes the substance's chemical structure, resulting in the formation of new substances. Changes like combustion, oxidation, or fermentation fall into this category, as they change the molecular makeup of the substance. Thermal change typically refers to temperature changes that could impact both physical and chemical processes but does not specifically denote a change in identity. Biological change pertains to living organisms and processes that might involve transformation but wouldn’t apply to the question about substance identity.

Thus, a physical change is distinguished by its preservation of the substance's identity despite alterations in its physical form.