Haber

From the Born-Haber cycle it follows that... 

Born-Haber cycle A thermodynamic cycle derived by application of Hess s law. Commonly used to calculate lattice energies of ionic solids and average bond energies of covalent compounds. E.g. NaCl ... 

Electron affinities may be estimated using a Born-Haber cycle. 

Haber process The process for the direct synthesis of ammonia from and Hj over a catalyst. 

Lattice energies may be derived from the Born-Haber cycle or calculated using the Kapustinskii equation. ... 

Haber J A, Gunda N V and Buhro WE 1998 Nanostruoture by design solution phase prooessing routes to nanoorystalline metals, oeramios, intermetallios and oomposites J. Aerosol Sol. 29 637... 

R. Kosloff, The Fritz Haber Research Center for Molecular Dynamics and Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel... 

Let us consider the formation of sodium chloride from its elements. An energy (enthalpy) diagram (called a Born-Haber cycle) for the reaction of sodium and chlorine is given in Figure 3.7. (As in the energy diagram for the formation of hydrogen chloride, an upward arrow represents an endothermic process and a downward arrow an exothermic process.)... 

The above Born-Haber cycle represents the enthalpy changes in the formation of an alkali metal halide MX from an alkali metal (Li. Na, K, Rb. Cs) and a halogen (Fj. CI2. Br2 or I2). 

This reaction is an undesirable side reaction in the manufacture of hydrogen but utilised as a means of removing traces of carbon monoxide left at the end of the second stage reaction. The gases are passed over a nickel catalyst at 450 K when traces of carbon monoxide form methane. (Methane does not poison the catalyst in the Haber process -carbon monoxide Joes.)... 

The production by this method was developed originally by Haber after whom the process is now named. Since the reaction is reversible... 

The process is as follows ammonia gas (made by the Haber process) is liquefied under pressure, to freeze out any water, and the anhydrous gas is then passed together with dust-free air through a... 

Although the left to right reaction is exothermic, hence giving a better equilibrium yield of sulphur trioxide at low temperatures, the reaction is carried out industrially at about 670-720 K. Furthermore, a better yield would be obtained at high pressure, but extra cost of plant does not apparently justify this. Thus the conditions are based on economic rather than theoretical grounds (cf Haber process). 

The enthalpies for the reactions of chlorine and fluorine are shown graphically in Figure 11.2 as the relevant parts of a Born-Haber cycle. Also included on the graph are the hydration energies of the two halogen ions and hence the enthalpy changes involved in the reactions... 

Department of Physical Chemistry, and Department of Biological Chemistry, The Fritz Haber Research Center, and the Wolfson Center for Applied Structural Biology, The Hebrew University, Jerusalem 91904, Israel Department de Physique, Department de Chimie, Universite de Montreal, Case Postale 6128, Succursale Centre-Ville, Montreal, Quebec, Canada H3C 3J7 Peptor Ltd., Kiryat Weizmann 16, Rehovot 76326, Israel... 

Ammonia (NH3) is the most important commercial compound of nitrogen. It is produced by the Haber Process. Natural gas (methane, CH4) is reacted with steam to produce carbon dioxide and hydrogen gas (H2) in a two step... 

J. Haber, The Role of Molybdenum in Catalysis, Climax Molybdenum Co. Ltd., London, 1981. 

The synthetic ammonia industry of the latter part of the twentieth century employs only the Haber-Bosch process (12—15), developed in Germany just before World War 1. Development of this process was aided by the concurrent development of a simple catalyzed process for the oxidation of ammonia to nitrate, needed at that time for the explosives industry. N2 and H2 are combined direcdy and equiUbrium is reached under appropriate operating conditions. The resultant gas stream contains ca 20% ammonia. 

When this reaction was first discovered, a considerably higher (ca 1300°C) temperature was required than that used in the 1990s. Thus, until Haber discovered the appropriate catalyst, this process was not commercially attractive. As of this writing (ca 1995), the process suffers from the requirement for significant quantities of nonrenewable fossil fuels. Although ammonia itself is commonly used as a fertilizer in the United States, elsewhere the ammonia is often converted into soHd or Hquid fertilizers, such as urea (qv), ammonium nitrate or sulfate, and various solutions (see Ammonium COMPOUNDS). 

Fig. 2. The Haber-Bosch process. Gases in parentheses are minor constituents of the mixture.

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