Refrigerator compressors and chemical hand warmers are both real-life examples of enthalpy. Both the vaporization of refrigerants in the compressor and the reaction to the iron oxidation in a hand warmer generate a change in heat content under constant pressure.Continue Reading
Despite the opposite results they give, both of these reactions obey the law of conservation of energy. When the refrigerant chemicals in the compressor are vaporized, heat is absorbed in an endothermic reaction. In the hand warmer, iron oxidation is an exothermic reaction that releases heat. The total amount of energy in both systems remains the same.
Temperature is a factor in determining enthalpy; the same reactants may transfer a different amount of heat in different ambient temperatures. The phases of matter involved also play a role in enthalpy. A substance with the same chemical composition does not necessarily transfer heat the same way following a phase change. Chemical equations dependent on enthalpy should state the temperature and phase needed for the reaction.
The number of steps in a reaction, or the order of these steps, does not change a reaction's enthalpy. A reaction using the same chemicals at the same temperature and pressure always results in the same amount of heat transfer. This principle is called "Hess' Law."Learn more about Thermodynamics