I have the equation Mg(OH)2 (s) -> Mg2+ (aq) + 2 OH- (aq) I started out with 20 drops of 1.0M MgCl2 in a well & 10 drops of .5M NaOH. Phenolphthalein was also added. When I heated the mixture, it became white, when it cooled it became pink. So, how can I tell if it was endo or exothermic? I want to say it was endothermic because it shifted to the reactant side when heated, but I'm not sure, almost doesn't seem right if you look at the original equation.