Gas solubilities in liquid water near the temperature of the density maximum, T _max(H₂O) = 277.13 K

Abstract

Liquid water has a density maximum at T _max(H₂O) = 277.13 K, and around this temperature the structure of the liquid changes significantly. In order to investigate the impact of such an unusual solvent density behavior upon the temperature dependence of Henry fugacities $h_{2,1} \left( {T,P} \right)$ (also known as Henry’s law constants) and related quantities of aqueous solutions of gases, that is, in particular, in order to solve the question of the existence of a point of inflection in curves $h_{2,1} \left( T \right)$ vs. T near T _max(H₂O), we use results of high-precision gas solubility measurements in water of He, Ne, Ar, N₂, and O₂, where $h_{2,1} \left( T \right)$ data have been reported for reasonably large and reasonably fine temperature grids around T _max(H₂O). Focusing on the temperature region $273.15 < {T \mathord{\left/ {\vphantom {T {{\text{K}} < 285}}} \right. \kern-0pt} {{\text{K}} < 285}}.15$, the discussion is essentially based on analysing difference quotient plots ${{\Delta \left( {\ln h_{2,1} } \right)} \mathord{\left/ {\vphantom {{\Delta \left( {\ln h_{2,1} } \right)} {\Delta \left( {{1 \mathord{\left/ {\vphantom {1 T}} \right. \kern-0pt} T}} \right)}}} \right. \kern-0pt} {\Delta \left( {{1 \mathord{\left/ {\vphantom {1 T}} \right. \kern-0pt} T}} \right)}}$ vs. $T_{\text{avg}}$. These plots summarize solubility results obtained at adjacent temperatures $T_{i}$ and $T_{i + 1}$, with $T_{\text{avg}} = {{\left( {T_{i} + T_{i + 1} } \right)} \mathord{\left/ {\vphantom {{\left( {T_{i} + T_{i + 1} } \right)} 2}} \right. \kern-0pt} 2}$ being the average temperature, and are closely related to plots of $\Delta H_{2}^{\infty } \left( {T_{\text{avg}} } \right)$ vs. $T_{\text{avg}}$, with $\Delta H_{2}^{\infty }$ being the partial molar enthalpy change on solution of the gas in water. The question is essentially resolved through including in the discussion insight gained from calorimetrically determined enthalpies of solution, i.e., through use of high-precision results obtained from flow-calorimeters originally designed by Gill and Wadsö in 1982 and 1984, respectively. Careful analysis of experimental results accumulated so far on the temperature dependence of the Henry fugacity around T _max(H₂O) and on corresponding enthalpies of solution do not support any unusual behavior of $h_{2,1}$ in this temperature region.

Graphical abstract