In chemistry, the Berthelot-Thomsen principle (or Thomsen-Berthelot principle) argued that heat of a reaction was the true measure of affinity and that the more heat release the greater the affinity of the reactants.  This is sometimes called the "heat theory of affinity". The Berthelot-Thomsen principle, in short, states that of all chemical reactions possible, the one developing the greatest amount of heat will take place, with certain obvious exceptions such as changes of state. 
The principle was proposed independently by Danish chemist Julius Thomsen in 1854 and by French chemist Marcellin Berthelot in 1864.  The principle was disproved in 1882 by German physicist Hermann Helmholtz in his "The Thermodynamics of Chemical Processes", which proved that, owing to the aspects of entropy, it is the free energy, not heat that is the measure affinities. 
1. Hall, Carl W. (2000). Laws and Models: Science, Engineering, and Technology (Berthelot-Thomsen principle, pg. 33). CRC Press.
2. Borisenko, Victor E. and Ossicini, Stefano. (2008). What is What in the Nanoworld (Berthelot-Thomsen principle, pg. 33). Wiley.
3. (a) Thomsen, Julius. (1854). “Die Grundzuge eines Thermochemischen Systems” (The Main Part of a Thermochemical Systems), Ann. Phys. 47, 34.
(b) Berthelot, Marcellin. (1873). “Sur la Statique de Dissolutions Salines” (On the Static Dissolutions of Salines), Bull. Soc. Chim. Pars 19, 160.
4. Helmholtz, Hermann. (1882). “On the Thermodynamics of Chemical Processes”, in: Physical Memoirs Selected and Translated from Foreign Sources, 1: 43-97. Physical Society of London, Taylor and Francis, 1888.
● Thomsen-Berthelot principle – Wikipedia.