Chemical reactions Haber process

As an example, consider the industrial synthesis of ammonia (NH3). Ammonia is made by the Haber process, a single chemical reaction between molecules of hydrogen (H2) and nitrogen (N2) Although it is simple, this synthesis has immense industrial importance. The United States produces more than 16 billion kilograms of ammonia annually. 

As an indispensable source of fertilizer, the Haber process is one of the most important reactions in industrial chemistry. Nevertheless, even under optimal conditions the yield of the ammonia synthesis in industrial reactors is only about 13%. This Is because the Haber process does not go to completion the net rate of producing ammonia reaches zero when substantial amounts of N2 and H2 are still present. At balance, the concentrations no longer change even though some of each starting material is still present. This balance point represents dynamic chemical equilibrium. 

In this chapter, we present basic features of chemical equilibrium. We explain why reactions such as the Haber process cannot go to completion. We also show why using catalysts and elevated temperatures can accelerate the rate of this reaction but cannot shift Its equilibrium position in favor of ammonia and why elevated temperature shifts the equilibrium In the wrong direction. In Chapters 17 and 18, we turn our attention specifically to applications of equilibria. Including acid-base chemistry. 

With the technical development achieved in the last 30 years, pressure has become a common variable in several chemical and biochemical laboratories. In addition to temperature, concentration, pH, solvent, ionic strength, etc., it helps provide a better understanding of structures and reactions in chemical, biochemical, catalytic-mechanistic studies and industrial applications. Two of the first industrial examples of the effect of pressure on reactions are the Haber process for the synthesis of ammonia and the conversion of carbon to diamond. The production of NH3 and synthetic diamonds illustrate completely different fields of use of high pressures the first application concerns reactions involving pressurized gases and the second deals with the effect of very high hydrostatic pressure on chemical reactions. High pressure analytical techniques have been developed for the majority of the physicochemical methods (spectroscopies e. g. NMR, IR, UV-visible and electrochemistry, flow methods, etc.). 

The importance of catalysts in chemical reactions cannot be overestimated. In the destruction of ozone previously mentioned, chlorine serves as a catalyst. Because of its detrimental effect to the environment, CFCs and other chlorine compounds have been banned internationally. Nearly every industrial chemical process is associated with numerous catalysts. These catalysts make the reactions commercially feasible, and chemists are continually searching for new catalysts. Some examples of important catalysts include iron, potassium oxide, and aluminum oxide in the Haber process to manufacture ammonia platinum and rhodium in the Ostwald synthesis of nitric... 

Students have already / v / employed Hess s law when performing Born-Haber cycle calculations in Chapter 6. 8.9 Hess s Law Now that we ve discussed in general terms the energy changes that occur during chemical reactions, let s look at a specific example in detail. In particular, let s look at the Haber process, the industrial method by which approximately 13 million tons of ammonia are produced each year in the United States, primarily for use as fertilizer. The reaction of hydrogen with nitrogen to make ammonia is exothermic, with AH0 = -92.2 kj. 

One of the principal goals of chemical synthesis is to maximize the conversion of reactants to products while minimizing the expenditure of energy. This objective is achieved easily if the reaction goes nearly to completion at mild temperature and pressure. If the reaction gives an equilibrium mixture that is rich in reactants and poor in products, however, then the experimental conditions must be adjusted. For example, in the Haber process for the synthesis of ammonia from N2 and H2 (Figure 13.7), the choice of experimental conditions is of real economic importance. Annual U.S. production of ammonia is about 13 million tons, primarily for use as fertilizer. 

Nitrogen In the production of ammonia by the Haber process (see p. 176) the ammonia is then used to make nitric acid, which is used in the manufacture of dyes, explosives and fertilisers In liquid form, as a refrigerant As an inert atmosphere for some processes and chemical reactions, because of its unreactive nature for example, empty oil tankers are filled with nitrogen to prevent fires In food packaging to keep the food fresh, for example in crisp packets where it also prevents the crisps being crushed (Figure 11.10)... 

Solution The Haber process is one of the most important industrial chemical reactions. The reaction describing the process can be written as... 

O chemical plant the reaction vessels and equipment for manufacturing chemicals O feedstock starting materials for chemical industrial processes O brine a concentrated solution of sodium chloride O Haber process the industrial process for the manufacture of ammonia O Contact process the industrial process for the manufacture of sulfuric aod... 

One of the main goals of chemical kinetics is to understand the steps by which a reaction takes place. This series of steps is called the reaction mechanism. Understanding the mechanism allows us to find ways to facilitate the reaction. For example, the Haber process for the production of ammonia requires high temperatures to achieve commercially feasible reaction rates. However, even higher temperatures (and more cost) would be required without the use of iron oxide, which speeds up the reaction. 

Metal surfaces have long been appreciated for their catalytic properties the ability to alter the pathways of important chemical reactions so as to increase reaction rates and selectivity for desired products well above the rates occurring in a homogeneous phase. Catalytic metals are widely utilized in a variety of chemical processes, and have been critical for processes that have had worldwide energy and health benefits, such as the petroleum refining process for fuel production, the Haber-Bosch... 

Ammonia is a very important industrial chemical that is used as a fertilizer and in the manufacture of many other chemicals. The reaction of nitrogen with hydrogen is a thermodynamically spontaneous reaction (product-favored), but without a catalyst it is very slow, even at high temperatures. The Haber process for its preparation involves the use of iron as a catalyst at 450°C to 500°C and high pressures. 

Knowing the factors that affect chemical equilibrium has great practical value for industrial applications, such as the synthesis of ammonia. The Haber process for synthesizing ammonia from molecular hydrogen and nitrogen uses a heterogeneous catalyst to speed up the reaction (see p. 540). Let us look at the equilibrium reaction for ammonia synthesis to determine whether there are factors that could be manipulated to enhance the yield. 

Transition metal complexes containing coordinated small molecules such as CO, 02, and N2 have been known for many decades and are of critical importance in industrial and biological processes and coordination chemistry as a whole (Table 1.1). Of all the industrially relevant molecules, H2 is arguably the most important. Catalytic hydrogenation reactions represent the most massive man-made chemical reactions in the world All crude oil is treated with hydrogen to remove sulfur and nitrogen in hydrodesulfurization/hydrodenitrogenation processes. Ten billion tons of ammonia is produced worldwide by the Haber process ... 

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