1. 8.3 Enthalpy YOU ARE EXPECTED TO BE ABLE TO:
Define enthalpy and distinguish enthalpy from energy.
Define DH for a process and relate the + or - value of DH to endothermic and exothermic reactions.
Chemistry 1011 Slot 5

2. Principle of Conservation of Energy
Energy can neither be created nor destroyed
All the heat energy flowing into (out of) a system from (to) the surroundings must go somewhere
In an endothermic process, it is used to increase the internal energy of the system and to allow the system to do work on its surroundings
q = DE + w
Chemistry 1011 Slot 5

3. Enthalpy
In most cases, reactions occur at constant pressure, so that we can write:
qp = DE + w
The heat added to or lost by a system at constant pressure is named the ENTHALPY change, symbolized by DH, so that
DH = qp = DE + w
Chemistry 1011 Slot 5

4. Enthalpy for Exothermic Reactions
Chemistry 1011 Slot 5