Diagram of the mechanism of the Haber process, showing how dihydrogen H2 and dinitrogen N2 react together over a substrate or catalyst of iron oxide, in a system heated and pressurized, the state of which works to form ammonia NH3 as a product. 
In his 1905 book Thermodynamics of Technical Gas Reactions, Haber recorded the production of small amounts of ammonia from N2 and H2 at a temperature of 1000° C with the help of iron as a catalyst.  Later he decided to attempt the synthesis of ammonia and this he accomplished after searches for suitable catalysts, by circulating nitrogen and hydrogen over the catalyst (iron plus a few oxides of potassium and aluminum) at a pressure of 150-200 atmospheres at a temperature of about 500° C. The following is an example Haber process reaction schematic: (Ѻ)
In this process, called "heterogeneous catalysis", the “surface” of the solid catalyst is the site of the reaction, in which the initial step involves the dissociation of N2 and H2 on the metal surface. In this state, the dissociated species are not truly free atoms because they are bonded to the metal surface, but are highly reactive. The two reactant molecules are said to “behave differently” on the catalyst surface, in the sense that the desired reaction is facilitated. 
The successful development of this process resulted in the establishment, with the cooperation of Bosch and Mittasch, of the Oppau and Leuna Ammonia Works, which enabled Germany to prolong the First World War when, in 1914, its supplies of nitrates for making explosives had failed. Modifications of this Haber process also provided ammonium sulphate for use as a fertilizer for the soil. The principle used for this process and the subsequent development of the control of catalytic reactions at high pressures and temperatures, led to the synthesis of methyl alcohol by Alwin Mittasch and to the hydrogenation of coal by the method of Bergius and the production of nitric acid.
Haber won the 1920 Nobel Prize in chemistry for this work. 
In human chemistry, the Haber process also serves as an excellent comparison model example of how human molecules (people) react differently together depending on which region of earth substrate (surface) the reaction takes place.  The crust of the earth, by comparison, is five percent iron and of the oxides embedded in it, sixteen percent are aluminum oxides and three percent are potassium oxides.
1. Haber, Fritz. (1905). Thermodynamics of Technical Gas Reactions, (Translator’s Preface, 1907, pg. vii). Longmans, Green, and Co.
2. Chang, Raymond. (1998). Chemistry, (pgs. 540-41, 585). McGraw-Hill.
3. Haber, Fritz. (1920). “The Synthesis of Ammonia from its Elements”, Nobel Lecture, June 02.
4. Thims, Libb. (2007). Human Chemistry (Volume One), (Haber process, pgs. 95-96), (preview), (Google books). Morrisville, NC: LuLu.
● Haber process – Wikipeda.
● Haber process – Ausetute.com
● Haber process (effect on fertilizers) – by Raymond Zmaczynski, Princeton.edu.