Temperature dependence of the heats of mixing aqueous alkaline earth chlorides

Two isolated systems in thermal equilibrium at constant pressure and coupled together do not normally exchange heat. Another way of saying the same thing is that the net change in heat between the coupled systems (at the same temperature) is zero. However, it is commonly known that when two or more electrolyte solutions are mixed together at the same temperature the net change in heat is in fact not zero, but some real quantity. This real value of heat has been explained variously as resulting from interactions between ions or interactions between ions and solvent molecules. Wood and Anderson1 studied heats of mixing alkaline earth halides at 25°C and interpreted their results in terms of such interactions. In using the Young-Wu-Krawetz2 model they classified the alkaline earth cations as structure makers in the face of solvent molecules, i.e. M2+ + solvent = M2+(solvent.