Chapter 4 - Enthalpy

Abstract

Enthalpy is the function of state and its value depends only on the starting and final state of the system. This chapter focuses on the application and determination of enthalpy. The heat measurement of various reactions is the first step in entering the realm of thermodynamics. The measurement of enthalpy, or heat, of different chemical processes is the objective of the first thermodynamic principle, the law of energy conservation. Every chemical process is connected with a certain amount of enthalpy, which the system receives from the surroundings. The reactions proceed at constant pressure so it is convenient to characterize the reaction by enthalpy change. The absolute values of the enthalpies or the internal energies, depends on the standard state, which are compared with the given quantity. The standard states mostly used are gases, liquids, and solids. There are different kinds of reaction enthalpy that is observed in molten salt chemistry, such as bonding energy, enthalpy of mixing, enthalpy of dissolution, and enthalpy of polymorphic transformation. The reliability of estimation of the enthalpy of fusion of the binary compounds and eutectic mixtures depends on the volume of input information, the choice of simplifying conditions, the difference between the melting points of the components and binary compounds, and the eutectic temperatures.