ABSTRACT
This chapter explores the definition of enthalpy and to the principles of the determination of its change accompanying a chemical reaction, carried out at constant pressure. It is a very important thermodynamic function. It relates heat quantities (including enthalpy changes) developed during a process to the temperature changes of the participating system. In fact, most biochemical and chemical reactions are carried out at constant pressure (most often at atmospheric pressure) and temperature. Thermal effects differ slightly. This is not the case when gases intervene because the volume change may be appreciable, but some corrections to the latest relation may be done by applying the perfect gas law.
