Twu, C.H., Coon, J.E. and Cunningham, J.R., 1993. An equation of state for hydrogen fluoride. Fluid Phase Equilibria 86: 47-62 Twu et al. (1992) [Twu, C.H., Coon, J.E. and Cunningham, J.R., 1992. An equation of state for carboxylic acids. Sixth International Conference on Fluid Properties and Phase Equilibria for Chemical Process Design, July 19–24, 1992 in Italy. Fluid Phase Equilibria, 82: 379-388] applied a generic cubic equation of state to carboxylic acids by taking association into account. The incorporation of chemical theory for carboxylic acids into the cubic equation of state was based on a monomer-dimer chemical equilibrium model. Hydrogen fluoride strongly associates by hydrogen bonding and strong evidence indicates that the vapor exists primarily as monomer and hexamer (Long et al., 1943 [Long, R.W., Hilderbrand, J.H. and Morrell, W.E., 1943. The polymerization of gaseous hydrogen and deuterium fluorides. J. Am. Chem. Soc., 65:182-187.]). Using the same approach as Twu et al. (1992), a monomer-hexamer chemical equilibrium model is built into a cubic equation of state to account for association of hydrogen fluoride. A closed-form equation of state is derived, which is written in terms of monomer parameters and the monomer-hexamer chemical equilibrium constant. This paper provides a new method for calculating the properties of HF. The calculated fugacity coefficient, vapor compressibility factor, heat of vaporization, and enthalpy departure of hydrogen fluoride exhibit significant deviations from ideal behavior. Failure to take this chemical association into account can lead to serious errors in vapor-liquid and liquid-liquid phase equilibrium and energy balance calculations.