What typically indicates a chemical change has occurred?

A change in color or state is a classic indicator of a chemical change because these alterations often signify that a new substance has been formed through the breaking and creating of chemical bonds during a reaction. For instance, if a colorless solution turns blue upon the addition of a reactant, this is evidence that a chemical reaction has taken place, resulting in the formation of a product with different properties. Similarly, a change in state, such as the production of a gas or a precipitate, can also indicate that a chemical change has occurred, highlighting the transformation of the original substances into something new.

In contrast, the other options do not signify a chemical change. When no change occurs in the original substances, it indicates that a physical change has happened, not a chemical one. If the substances become evenly mixed, this describes a physical mixing, rather than a chemical reaction where new bonds and substances are formed. Lastly, if the temperature remains constant during a process, it typically suggests that there is no significant energy change associated with a chemical reaction, which usually involves either an endothermic or exothermic process that alters temperature. Therefore, the correct answer underscores the observable transformations that suggest a chemical reaction has occurred.