ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

The term that refers to a property that cannot be observed without changing the identity of a substance is "chemical property." A chemical property describes the ability of a substance to undergo a specific chemical change or reaction. This involves interactions with other substances, which often results in the formation of new substances with different properties.

For example, the flammability of a substance is a chemical property. When a substance burns, it reacts with oxygen in the air, producing different products (like carbon dioxide and water), thus changing the identity of the original substance.

In contrast, physical properties can be observed without altering the substance's identity. These include characteristics such as color, melting point, and boiling point, which do not involve any chemical change. Intensive properties, which depend on the type of material rather than the amount, and extensive properties, which do depend on the amount of the material, both relate to physical characteristics rather than the inherent chemical reactivity of a substance.