A change in temperature alone is not necessarily a chemical reaction. While temperature changes can indicate that a chemical reaction is occurring, they can also result from physical changes.
For instance, when a chemical reaction takes place, such as combustion, the reaction often releases or absorbs heat, causing the temperature to change. This is noticeable in exothermic reactions, where heat is released, and in endothermic reactions, where heat is absorbed.
However, a temperature change can also occur during physical processes like melting, freezing, or boiling, which do not involve a chemical change. For example, when ice melts into water, heat is absorbed, but the chemical composition remains H2O throughout the process.
In summary, while a change in temperature can be a sign of a chemical reaction, it is not definitive proof of one. To confirm a chemical reaction, one must also consider changes in chemical composition and the formation of new substances.