Delta H

[Tiffany_Cacy_3D]

During the last bit of class we talked about exo- and endothermic reactions and how this is determined by delta H. What is delta H and if it is positive does that mean it is always going to endothermic and favor the products when heat is added? If it is negative does it always mean it is exothermic and favors reactants when heat is added? If heat was lowered would both of them favor the opposite as they do if heat is added?

[WilliamNguyen_4L]

Delta H is the change in enthalpy of a system. When Delta H is positive that means the heat is going into the system and so what that means is that heat is required to create the product and so the reaction is endothermic. When delta H is negative that means that heat is leaving the system so heat is a product of the reaction and it is exothermic. If you think of heat as a reactant in an endothermic reaction and as a product in an exothermic reaction then it becomes clear which side is favored when adding heat. In an endothermic reaction adding heat is the same as adding reactant so then the products are favored. In an exothermic reaction adding heat is the same as adding product so the reactants are favored. Conversely, cooling is like taking away heat so the effects will be the opposite of adding heat.

[John_Richey_4A]

H is the amount of energy in a system plus the product of its pressure and volume, so delta H would basically be how much energy was taken away or put into the system. If its positive that means the system absorbed heat and would always favor the products when heat is added and visa versa for your second question. For your last question, it would favor it more than it had previously when there was more heat.