Henri Le Châtelier (1850-1936), a French chemist, first stated the rule known as Le Châtelier's Principle in 1884. The principle states that if an external change is imposed on a system in reactive equilibrium, the system will establish a new equilibrium, which counteracts the external change. Le Châtelier's principle was fully explained in an 1888 paper. This fundamental contribution to chemical thermodynamics had been anticipated in part by J. W. Gibbs, whose work Le Châtelier translated into French, helping Gibbs' ideas reach a broader audience. Le Châtelier also suggested the use of a thermocouple to measure high temperatures, and invented the optical pyrometer, a thermometer that uses infrared radiation to determine an object’s temperature by measuring the wavelength of the radiation emitted.
- Chemguide. Le Châtelier's Principle