Temperature change

The useful clue here is the temperature change of the surroundings. In a simple investigation, a thermometer in the reaction mixture shows whether the liquid around the reacting particles has warmed or cooled. Energy transferred to those surroundings makes the reading rise; energy taken from them makes it fall.

Ions combine to form an insoluble solid, and the accompanying temperature change is recorded.

A temperature change alone does not tell you how much energy was transferred. Also, a reaction may need an initial input of energy to get started without being endothermic overall: a flame ignites a fuel, but burning then transfers energy to the surroundings.

The temperature change is