Determination of ΔH for Reactions of the Born-Haber Cycle

The Born-Haber cycle is a useful framework for discussing the formation of ionic compounds from their elements. The cycle separates the overall formation reaction into a series of steps whose DeltaH values are individually determined. This paper reviews the many experimental methods used to determine DeltaH for the various steps of the cycle for the formation of sodium chloride. The methods employed are surprisingly varied: they include vapor pressure measurements, several forms of spectroscopy, and various types of calorimetry. The cycle is constructed using the best available data from the current literature. Particular care is taken to specify the standard state of each species involved and to assign every reaction its proper enthalpy change, rather than its energy change. Two topics given special attention are the choice of standard state of the electron and the importance of distinguishing lattice enthalpy from lattice energy.