Gibbs Energy and Helmholtz Energy: Liquids, Solutions and Vapours
CHAPTER 15: Experimental Determination of Vapor Pressures
Published:08 Sep 2021
D. H. Zaitsau and E. Paulechka, in Gibbs Energy and Helmholtz Energy: Liquids, Solutions and Vapours, ed. E. Wilhelm and T. M. Letcher, The Royal Society of Chemistry, 2021, pp. 425-448.
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For pure compounds, vapor pressure is equivalent to the equilibrium constant of the evaporation process. Hence it can be directly used to determine the change in the standard Gibbs energy on going from the condensed phase to the gas phase. Tensimetric methods started from simple manometric measurements for water in the mid-nineteenth century. Today, vapor pressures can be measured from the sub-millipascal range to the critical point. The normal boiling points of thermally unstable compounds have become available. A general trend is to make the measurements faster while keeping the uncertainty at a reasonable level. This chapter is focused on recent developments in the field, including static instruments with modern pressure detectors and techniques using differential scanning calorimetry and thermogravimetric analysis. Both advantages and challenges of these methods are discussed.