This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 edition. Excerpt: ...temperatures. With change of temperature the equilibrium of any reaction is shifted in a way that can be definitely predicted from its heat of reaction. If heat is given out when a substance is formed, heat will be absorbed when the same substance is decomposed. When we raise the temperature of a system in ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 edition. Excerpt: ...temperatures. With change of temperature the equilibrium of any reaction is shifted in a way that can be definitely predicted from its heat of reaction. If heat is given out when a substance is formed, heat will be absorbed when the same substance is decomposed. When we raise the temperature of a system in equilibrium, the state of equilibrium shifts in such a way that heat is absorbed (288, 367). The heat of formation (361) of NH3 is 12,200 calories: 3Hj+N2-2NH3+2X 12,200 cal. Therefore the higher the temperature the smaller the proportion of NH3 present in the equilibrium mixture, and vice versa, as shown by the following table, in which is given the percentage of NH3 at various temperatures and one atmosphere pressure: Temperature Per Cent of NHi 800 O.OI 6oo 0.05 400....0.48 It is evident that the lower the temperature the more favorable the result; but a serious practical difficulty is encountered if one tries to make NH3 at low temperatures; the union of H2 and N2 proceeds the more slowly the lower the temperature, so that at 4000 it would require days for equilibrium to be reached. In this respect this reaction is like all others; the speed of reaction, other things being equal, is slower the lower the temperature. The experimenter then faces this dilemma: at a high temperature the reaction gives very little NH3; at a low temperature it goes too slowly. Is there no way to surmount this difficulty? Is there no way to hasten a reaction except by increasing the temperature? Yes, there is, and this by means of a catalytic agent! 522. Catalytic Agents for the Ammonia Reaction.--As illustrations of cases of catalysis we may recall that CuCl2 catalyzes the reaction 4HCl+02-2H20+2Cl2; (239) that Mn02 promotes the decomposition of KCl03 (306); and...
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