勒夏特列原理Le Chatelier's principle

增大反应物浓度，平衡向生成物方向移动；增大压强，平衡向气体分子数减少的方向移动；升高温度，平衡向吸热方向移动。浓度和压强的改变只改变反应商 Q，平衡常数 K 不变；只有温度会改变 K 本身。催化剂同等加快正逆反应，不使平衡移动。

Adding reactant shifts the equilibrium toward products; raising the pressure shifts it toward fewer moles of gas; raising the temperature shifts it in the endothermic direction. Changes in concentration and pressure alter only the reaction quotient Q, not the equilibrium constant K; only temperature changes K itself. A catalyst speeds forward and reverse reactions equally and does not shift the equilibrium.

法国化学家亨利·勒夏特列在 1884 年提出这一规律，并于 1888 年给出更一般的表述。荷兰化学家范特霍夫在 1884 年也独立给出了温度对平衡影响的规律，德国物理学家布劳恩于 1887 年提出类似的物理表述，因此又称勒夏特列-布劳恩原理。

French chemist Henry Le Chatelier stated the rule in 1884 and gave a more general form in 1888. Van 't Hoff independently described the effect of temperature on equilibrium in 1884, and the German physicist Braun proposed a similar physical statement in 1887, which is why it is also called the Le Chatelier–Braun principle.

原理的严格依据是 ΔG° = −RT ln K 和范特霍夫方程 d ln K/dT = ΔH°/RT²。它是定性规则，存在反例：恒温恒压下向 N₂ + 3H₂ ⇌ 2NH₃ 体系加入 N₂，在某些组成下平衡反而向生成 N₂ 的方向移动；恒容加入惰性气体则平衡不移动。定量判断应比较 Q 与 K。

Its rigorous basis is ΔG° = −RT ln K together with the van 't Hoff equation d ln K/dT = ΔH°/RT². It is qualitative and has exceptions: adding N₂ at constant temperature and pressure to N₂ + 3H₂ ⇌ 2NH₃ can, at some compositions, shift the equilibrium toward forming more N₂, and adding an inert gas at constant volume does not shift it at all. For quantitative work compare Q with K.

哈伯法合成氨采用高压、及时分离氨来提高转化率，同时在约 450 °C 下兼顾速率与平衡。接触法制硫酸、酯化反应中用过量醇或除水，都是利用该原理提高产率。生理上，血液中 CO₂、H₂CO₃ 与 HCO₃⁻ 的平衡调节也可用它解释。

The Haber process uses high pressure and removes ammonia as it forms to raise conversion, while running near 450 °C to balance rate against equilibrium. The contact process and esterifications driven by excess alcohol or water removal use the same principle to raise yield. In physiology it explains how the CO₂ / H₂CO₃ / HCO₃⁻ equilibrium in blood responds to change.