06413_08 - H Haber, Fritz (18681934) German chemist who...

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H Haber, Fritz (1868–1934) German chemist who worked at the Karlsruhe Technical Institute, where he developed the * Haber process in 1908. As a Jew, he left Germany in 1933 to go into exile in Britain, working in Cambridge at the Cavendish Laboratory. For his Haber pro- cess, he was awarded the 1918 Nobel Prize for chemistry. Haber process An industrial process for producing ammonia by reaction of ni- trogen with hydrogen: N 2 + 3H 2 ˆ 2NH 3 The reaction is reversible and exother- mic, so that a high yield of ammonia is favoured by low temperature ( see le chatelier’s principle ). However, the rate of reaction would be too slow for equilib- rium to be reached at normal tempera- tures, so an optimum temperature of about 450 ° C is used, with a catalyst of iron containing potassium and alu- minium oxide promoters. The higher the pressure the greater the yield, although there are technical dif Ü culties in using very high pressures. A pressure of about 250 atmospheres is commonly employed. The process is of immense importance for the Ü xation of nitrogen for fertilizers. It was developed in 1908 by Fritz Haber and was developed for industrial use by Carl Bosch (1874–1940), hence the alter- native name Haber–Bosch process . The nitrogen is obtained from liquid air. For- merly, the hydrogen was from * water gas and the water-gas shift reaction (the Bosch process ) but now the raw material (called synthesis gas ) is obtained by steam * reforming natural gas. habit See crystal . habitat The place in which an organ- ism lives, which is characterized by its physical features or by the dominant plant types. Freshwater habitats, for ex- ample, include streams, ponds, rivers, and lakes. See also microhabitat . habituation 1. A simple type of learn- ing consisting of a gradual waning in the response of an animal to a continuous or repeated stimulus that is not associated with * reinforcement. 2. The condition of being psychologically, but not physically, dependent on a drug. Hadean The earliest eon in the history of the earth, from the time of the accre- tion of planetary material, around 4600 million years ago, to the date of the old- est known rocks – and hence the begin- ning of the geological record – about 3800 million years ago. The young earth was probably a rocky planet with a hot interior and a moist surface with oceans of liquid water. No evidence of life has been found. Compare archaean . hadron Any of a class of subatomic par- ticles that interact by the strong interac- tion ( see fundamental interactions ). The class includes protons, neutrons, and pions. Hadrons are believed to have an in- ternal structure and to consist of quarks; they are therefore not truly elementary. Hadrons are either * baryons, which decay into protons and are believed to consist of three quarks, or * mesons, which decay into * leptons and photons or into proton pairs and are believed to consist of a quark and an antiquark. See elementary particles .
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06413_08 - H Haber, Fritz (18681934) German chemist who...

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