含义Meaning
一定温度下，稀溶液中挥发性溶质的平衡分压与其浓度成正比；常用于气体在液体中的溶解度。
At fixed temperature the vapour pressure of a dilute volatile solute is proportional to its concentration — the law of gas solubility.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(k_x\) | 亨利常数（摩尔分数形式）Henry constant (mole-fraction form) | Pa |
| \(k_\mathrm{H}\) | 亨利溶解度常数Henry solubility constant | mol·L⁻¹·Pa⁻¹ |
推导Derivation
极稀时每个溶质分子周围全是溶剂，其逸出倾向与浓度成正比，但比例常数不是 \(p_\mathrm{B}^*\)，而由溶质–溶剂作用决定。
At infinite dilution each solute molecule is surrounded by solvent, so its escaping tendency is proportional to concentration — with a constant set by solute–solvent interactions, not \(p_\mathrm{B}^*\).
由吉布斯–杜亥姆方程可证：溶剂服从拉乌尔定律的浓度区间内，溶质服从亨利定律。
Gibbs–Duhem shows that where the solvent obeys Raoult’s law the solute obeys Henry’s law.
温度升高，气体溶解度一般降低（溶解放热，范特霍夫关系）。
Gas solubility usually falls with temperature (exothermic dissolution).
适用条件与局限Assumptions & limitations
只适用于稀溶液，且溶质在气、液两相中的分子形态相同；与溶剂反应的气体（NH₃、CO₂ 的水合、HCl）偏离很大。
Dilute solutions only, same molecular form in both phases; gases that react with the solvent (NH₃, HCl) deviate strongly.
亨利常数有多种定义和单位，引用时必须注明。
Henry constants come in many conventions — always state which.
例题Worked example
潜水减压病：高压下 N₂ 溶入血液更多，快速上浮时析出气泡。
Decompression sickness: more N₂ dissolves in blood at depth and bubbles out on rapid ascent.