What observations help us determine whether a chemical reaction has taken place?

There are several observations that can be made to determine if a chemical reaction has occurred. The first is a change in temperature. Heat can be absorbed (endothermic reaction) or released (exothermic reaction) which results in a temperature change. This can be noted with a thermometer. Reactions can also have a color change. A change in color represents a chemical reaction. Another observation is if there is a smell or odor after the reaction takes place. When a reaction takes place, gases can sometimes be removed from the system. This can be observed by the formation of bubbles. Another observation is the formation of a precipitate. This is a solid that forms out of solution. When a solute is dissolved in a solution, a chemical reaction took place. Lastly, if there is a change in pH a chemical reaction took place. This will need to be tested with pH strips.