Harper College explains that forming a precipitate, color changes, gas formation and temperature change are signs of a chemical change. The University of California, Davis adds that the presence of odor also indicates a chemical change. There are only five indicators of a chemical change.
The University of California, Davis explains the a change in temperature is a clear indicator that a chemical change has occurred. Heat is a product of the reaction and is called an exothermic reaction.
Harper College states that when a gas forms after two substances have been combined, it is clear that a chemical reaction has occurred. The gas is a product of the reaction.
If two chemicals are combined and a new color forms, then a chemical reaction has occurred. Harper College explains that this indicates a chemical change as long as the color change is not a result of a dilution.
The University of California, Davis explains that the presence of an odor indicates a chemical change. For example, when an egg begins to smell, a change in the chemical composition of the egg has occurred.
A precipitate indicates a chemical change. Harper College states that a precipitate forms when two substances react together to form a new substance.