Thermodynamics is the study of energy transformations. Energy is defined as the ability to do work in physics. In chemistry, work is defined as directed energy change resulting from a process. Teo common forms of energy in chemistry are kinetic energy and potential energy. In a reaction, if there is an output of energy out of the system, then the reaction is exothermic. If there is an input of energy into the system, then the reaction is endothermic.