If the process is endothermic, the heat transfer required for the process to take place is that which is absorbed from the solution, and the temp. If the process is exothermic, the heat transferred by the process is trapped in the solution and the temperature of the solution increases. Two reagents at 25 o C are mixed together in a calorimeter to form 50.8 g of aqueous reaction solution. The temp. dropped from 25.0 to 19.6 o C when the reaction occurred. The reaction is endothermic.
Every reaction gives a H .
A reaction always gives the difference between 2 or more enthalpies, neither of which is known. For many reactions we can measure H directly. When reactants are converted to products, the change in the enthalpy is the same whether the reaction takes place in one step or in a series of steps. H is a state function. In thermodynamics, capital letters like H indicate state functions.