A simple polystyrene calorimeter of low heat capacity can be used for any non–combustion reaction that will happen spontaneously at room temperature involving liquids or solid reacting with a liquid and it doesn't matter if the reaction is exothermic or endothermic. Although it ignores the heat absorbed by the thermometer, reasonably accurate results can be obtained for a school/college laboratory. The reactants are weighed in if solid and a known volume of any liquid (usually water or aqueous solution). The mixture could be a salt and water (heat change on dissolving) or an acid and an alkali solution (heat change of neutralisation). It doesn't matter whether the change is exothermic (heat released or given out, temperature increases) or endothermic (heat absorbed or taken in, temperature decreases).