So in the case of
1. MgSo4 in H20 the solution formation = -91 kj/mol (exothermic)
2. NH4NO3 in H20 the solution formation = +26 kj/mol (endothermic)
According to my professor both are solutions. Now what i don't understand is, how can I be able to tell if both not only one is a solution. Because I know that exothermic reactions tend to be solutions. But in the case of a endothermic solution, how is this possible?
I know it has something to do with entropy and enthalpy. But lets on an exam, how will I be able to tell?