What is the term for the properties of a substance that can be observed without changing its chemical composition?

The term for properties of a substance that can be observed without changing its chemical composition is indeed physical properties. Physical properties include characteristics such as color, melting point, boiling point, density, and solubility, which can be measured or observed without altering the substance's molecular structure.

For instance, if you take a solid ice cube and observe its color and shape, or measure its temperature, you’re assessing its physical properties. When you melt the ice, it turns into water, but its chemical composition (H₂O) remains unchanged.

Other terms presented, such as chemical properties, refer to aspects of a substance that can only be observed during a chemical reaction, which alters its molecular makeup. Thermodynamic properties usually describe the energy and heat of a system, focusing on statistical mechanics or macroscopic reviews of substances under various conditions. Reactive properties can indicate how a substance would behave under certain reactions, implying an irreversible change to its chemical structure.