化学平衡Chemical equilibrium

对反应 aA + bB ⇌ cC + dD，平衡时 K = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ 为常数（质量作用定律），只与温度有关。热力学上 ΔrG° = −RT ln K；任意时刻反应商 Q 与 K 比较可判断方向：Q < K 正向进行，Q = K 达到平衡，Q > K 逆向进行。平衡状态与从哪一侧开始无关。

For aA + bB ⇌ cC + dD, at equilibrium K = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ is a constant depending only on temperature (the law of mass action). Thermodynamically ΔrG° = −RT ln K, and comparing the reaction quotient Q with K gives the direction: Q < K runs forward, Q = K is at equilibrium, Q > K runs backward. The equilibrium state is the same whichever side it is approached from.

1803 年贝托莱在埃及观察到盐湖边 Na₂CO₃ 的生成，意识到反应方向受物质数量影响。1864 年挪威的古德贝格和瓦格提出质量作用定律。1884 年范特霍夫给出平衡常数与温度的关系，同年勒夏特列提出平衡移动原理；1870 年代吉布斯建立的化学势理论为化学平衡提供了严格的热力学基础。

In 1803 Berthollet, seeing Na₂CO₃ form on the shores of Egyptian salt lakes, realised that the direction of a reaction depends on the amounts present. In 1864 the Norwegians Guldberg and Waage proposed the law of mass action. In 1884 van 't Hoff related equilibrium constants to temperature and Le Chatelier gave his principle, while Gibbs's theory of chemical potential in the 1870s provided the rigorous thermodynamic foundation.

化学平衡包括电离平衡（Ka、Kb、Kw）、沉淀溶解平衡（Ksp）、配位平衡（K稳）和气相平衡（Kp）等。工业上通过控制温度、压强和浓度，使合成氨、制硫酸、酯化等反应获得较高产率；生物体内的血液缓冲体系、氧合血红蛋白的结合与释放也遵循平衡原理。

Equilibria include ionisation (Ka, Kb, Kw), solubility (Ksp), complex formation (stability constants) and gas-phase equilibria (Kp). Industry controls temperature, pressure and concentration to obtain high yields in ammonia synthesis, sulfuric acid manufacture and esterification; in the body, blood buffering and the loading and unloading of oxygen by haemoglobin follow the same principles.