Temperature dependence of Henry’s law constant in an extended temperature range

The Henry’s law constants H for chloroform, 1,1-dichloroethane, 1,2-dichloropropane, trichloroethene, chlorobenzene, benzene and toluene were determined by the EPICS-SPME technique (equilibrium partitioning in closed systems––solid phase microextraction) in the temperature range 275–343 K. The curvature observed in the lnH vs. 1=T plot was due to the temperature dependence of the change in enthalpy DH0 during the transfer of 1 mol solute from the aqueous solution to the gas phase. The nonlinearity of the plot was explained by means of a thermodynamic model which involves the temperature dependence of DH0 of the compounds and the thermal expansion of water in the threeparameter equation ln ðHqT TÞ ¼ A2=T þ BTB þ C2, where qT is the density of water at temperature T, TB ¼ lnðT =298Þþ ð298 T Þ=T , A2 ¼ DH0 298=R, DH0 298 is the DH0 value at 298 K, B ¼ DC0 p=R, and C2 is a constant. DC0 p is the molar heat capacity change in volatilization from the aqueous solution. A statistical comparison of the two models demonstrates the superiority of the three-parameter equation over the two-parameter one lnH vs. 1=T ). The new, three-parameter equation allows a more accurate description of the temperature dependence of H, and of the solubility of volatile organic compounds in water at higher temperatures.