What is an indicator of a chemical change, particularly in the context of energy?

A temperature increase or decrease is a key indicator of a chemical change because it signifies that energy is being absorbed or released during the process. This energy transformation often results from the breaking and forming of chemical bonds, which alters the energy states of the reactants and products involved in the reaction. For example, in exothermic reactions, energy is released as heat, which raises the temperature, whereas in endothermic reactions, energy is absorbed, leading to a decrease in temperature.

While physical state changes and volume changes can occur during chemical reactions, they are not exclusive to chemical changes. Physical processes, such as melting, boiling, or dissolving, can also involve these changes without any chemical transformation. Therefore, temperature change stands out as a more definitive indicator of a chemical change, as it directly relates to the energy dynamics at play during the reaction.