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Electron transfer reactions in .NET Printing Code 3/9 in .NET Electron transfer reactions




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12.2 Electron transfer reactions using barcode writer for none control to generate, create none image in none applications. .NET Framework 4.0 You may not have none none noticed it, but we have considered two kinds of reactions in previous chapters. In some, such as (9.3),.

SiO2 s + 2H2 O = H4 SiO4 aq 335 Redox reactions all elements on the right side have the same number of electrons that they have on the left side there is no change in valence of any element. In others, such as (9.16),.

CH4 g + O2 g = CO2 g + 2 H2 g there is such a change. For example, the carbon in CH4 is C4 , and the carbon in CO2 is C4+ . Each carbon atom in methane that changes to a carbon atom in carbon dioxide must get rid of eight electrons it is oxidized.

Where do the electrons go Obviously, they go to the other actors in the reaction. Oxygen in O2 has a valence of zero (O0 ), while in carbon dioxide it is 2 (O2 ), so in changing from O2 to CO2 , two oxygens gain four electrons. The other four electrons go to hydrogen, which has a valence of +1 (H+ ) in methane and zero in hydrogen gas.

Both oxygen and hydrogen are reduced, if the reaction goes from left to right as written. Similarly in reaction (9.15),.

6 Fe2 O3 s = 4 Fe3 O4 s + O2 g we see that all of the iron atoms in Fe2 O3 are ferric iron (Fe3+ ), while one out of three iron atoms in Fe3 O4 is ferrous iron (Fe2+ ). The iron is partially reduced, while some oxygen in Fe2 O3 is oxidized to O2 g there is a transfer of electrons from iron to oxygen, or from oxygen to iron, depending on which way the reaction goes. Without such electron transfers, these and many other reactions, including many necessary to life processes, could not proceed.

. 12.3 The role of oxygen Both of our exam ples involve oxygen, which is the most common oxidizing agent in natural systems. In the presence of oxygen, many elements are oxidized (lose electrons, gain in valence), while oxygen is reduced. You need only think of rusty nails, green staining on copper objects, and burning logs to realize the truth of this.

The process of oxidation obviously takes its name from the fact that oxygen is the premier oxidizing agent, but it is actually defined in terms of electron loss, or increase in valence. In other words, the electrons need not come from or go to oxygen; many redox reactions take place without oxygen. Consider, for example, what happens when you put a piece of iron in a solution of copper sulfate (Figure 12.

1). After a while you see the characteristic color of metallic copper forming on the surface of the iron, and the iron gradually crumbles and eventually disappears. Metallic copper precipitates, and iron dissolves.

The reaction is essentially. Cu2+ + Fe Cu + Fe2+ (12.1). We need not incl ude the sulfate, because it is not involved in this process being negatively charged, the SO2 ions provide an overall charge balance in 4. 12.3 The role of oxygen Figure 12.1 An iron nail in a solution of copper sulfate. Cu2+ Fe2+ the solution. In none for none this example, copper is reduced and iron is oxidized, without the aid of oxygen. (Of course, if we wait long enough, and our solution is open to the atmosphere, oxygen dissolved in the solution will eventually oxidize the copper and the ferrous iron.

) What does thermodynamics tell us about this reaction Looking up the data from Appendix B, we find. f GCu f GFe2+ f GCu2+ f GFe = 0 + 78 90 65 49 0 = 144 390 kJ mol 1 = 144 390 J mol 1 This means that none none with both metallic copper and iron present, and cupric and ferrous ions present at 1 molal concentration (and acting ideally), the reaction would proceed spontaneously, as observed. But more interestingly,. = RT ln K 144 390 = 8 3 none for none 145 298 15 ln K log K = 144 390/ 2 302 59 8 3145 298 15 = 25 295. Thus K= aFe2+ aCu2+ = 1025 295. Redox reactions This means that to reach equilibrium, the activity ( concentration) of Fe2+ would have to be enormously greater than that of the Cu2+ , so the reaction will always proceed as written, and cannot be made to go the other way (at least, not by simply adjusting the ion concentrations)..
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