PB=Kx，B xB
PB=Kb，B bB
PB=Kc，B cB
Where pB is the vapor partial pressure of solute in dilute solution; XB is the content fraction of solute; K is Henry constant, and its value is related to temperature, solute and solvent properties, and Henry coefficient is basically unaffected by pressure.
Because the scale of solution composition in Henry's law is different, the unit of Henry coefficient is different, and the value of the same solute in the same solvent is different at a certain temperature. When the above formula is expressed by xB (molar fraction of solute B), bB (molar concentration of substance) or cB (molar concentration of substance), the value of k will change. The units of Kx, Kb and Kc are Pa, pamol-1,pa mo l- 1 DM 3 respectively.
Henry's law can only be applied when the molecular state of solute in gas phase and liquid phase is the same. If solute molecules dissociate and associate in solution, xB (or mB, cB, etc. In the above formula) shall refer to the content of the part with the same molecular state in the gas phase; When the total pressure is not large, if multiple gases are dissolved in the same liquid at the same time, Henry's law can be applied to any one of them respectively; Generally speaking, the thinner the solution, the more accurate Henry's law, and the solute can strictly abide by the law when xB→0.
Extended data:
Henry's coefficient is different at different temperatures. With the increase of temperature, the volatilization ability of volatile solute increases and Henry coefficient increases. In other words, under the same partial pressure, the solubility of gas decreases with the increase of temperature.
If several gases are dissolved in the same solvent at the same time to form a dilute solution, Henry's law applies to the relationship between the equilibrium partial pressure of each gas and its solubility. The dissolution of N2 and O2 in air in water is one such example.
Henry constant can also be used as a physical constant to describe the distribution ability of compounds in gas-liquid two-phase, and the migration direction and speed of organic matter in gas-liquid two-phase mainly depend on Henry constant. According to the Henry constant of organic matter, we can judge the solubility of gas in liquid (when the temperature is constant, the one with larger Henry constant is difficult to dissolve in the same solvent), the volatilization of liquid and the migration and trend in multi-media environment.
Henry constant is also a key parameter in the process of environmental remediation and adsorption equilibrium, which is widely used in environmental science and engineering. At present, the main methods to determine Henry's constant are static equilibrium method, chromatography, quantitative structure-property correlation method, etc. These methods are all calculated by using the equilibrium headspace concentration ratio.
Baidu encyclopedia-Henry's law