In 1905, Haber, in his Thermodynamics of Technical Gas Phase Reactions, did some of the first preliminary on calculating the free energies of formations of chemical substances. This was a big stepping stone to Gilbert Lewis' 1923 Thermodynamics and the Free Energy of Chemical Substances.
In 1907, Haber developed a method to successfully synthesize ammonia , from nitrogen and and hydrogen gas reactants, a difficult reaction in that it required the breaking of the strong nitrogen triple bond N≡N:
Thereafter, fertilizer became readily available for the world, and a global population explosion resulted.
Quotes | On
The following are quotes:
- "Haber’s Thermodynamics of Technical Gas Phase Reactions  is the most important contribution to the subject of predicting the course of a chemical reaction from a few characteristic constants of the reacting substances, after the ill-starred attempt of Berthelot.”
- — Arthur Lamb (1907), “Translators Preface” 
- Haber, Fritz. (1905). Thermodynamics of Technical Gas Reactions (Translator’s Preface, pg. vii). Longmans, 1907.
- Fritz Haber – Hmolpedia 2020.