Complexity in Chemical Reactions

This section discusses entropy production in a specific context. Owing to the complexity of the matter we shall focus on processes describable entirely in terms of the last line in Table7.2. This certainly is crude, because chemical reactions always involve other types of currents and forces as well. 

Momentarily we are interested in the process far from equilibrium and we neglect the reverse reaction. Suppose that the reaction rate is given by 

A fluctuation of the amount of X thus gives rise to the entropy production 

It looks as if in this case there is the danger of an unstable process. We shall see that things return to normal, i.e. stability, when we analyze this more carefully. However, what is important to remember is that autocatalytic reactions are special and, as it turns out, are a key ingredient to the explanation of the creation of order not possible in systems remaining close to equilibrium.  

The following system of coupled reactions, which has a realistic origin (Ebeling and Feistel 1986), here serves to illustrate a number of important aspects of non-linearity and autocatalysis. Most important, perhaps, is the possibility of bifurcation providing systems with the choice between different steady states. This in principle offers the possibility for competing alternative pathways along which chemical systems can evolve and (sometimes) compete along the way. 

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Eyring H 1934 The activated complex in chemical reactions J. Chem. Phys. 3 107... 

Eyring H 1935 The activated complex in chemical reactions J. Chem. Phys. 3 107-15 Hofacker L 1963 Quantentheorie chemischer Reaktionen Z. Naturf. A 18 607-19 Robinson P J and Holbrook K A 1972 Unimolecular Reactions (New York Wiley)... 

Elcombe MM, Pryor AW (1970) The lattice dynamics calcium fluoride. J Phys C 3 492-499 Eyring H (1935) The activated complex in chemical reactions. J Chem Phys 3 107-117 Earquhar J, Bao HM, Thiemens M (2000) Atmospheric influence of Earth s earliest sulfur cycle. Science 289 756-758... 

Eyring H. The activated complex in chemical reactions. J Chem Phys 1935 3 107-115. 

H. Eyring. The Activated Complex in Chemical Reactions. J. Chem. Phys., 3 107-114,1935. 

H. Eyring, M. Polanyi, Simple Gas Reactions. Z. Phys. Chem. B, 1931, 12, 279-311 H. Eyring, Activated Complex in Chemical Reactions. J. Chem. Phys. 1935, 3, 107-115 H. Eyring, The Activated Complex and the Absolute Rate of Chemical Reactions. Chem. Rev. 1935, 17, 65-77. 

One of the characteristic features of the metal-bis-acetylide complexes in chemical reactions is that they undergo a ligand exchange reaction with metal dihalides in amines in the presence of a cuprous halide catalyst to produce a monoalkynyl-metal-monohalide complex (Eq. IS) which results from selective cleavage of the metal-carbon bond weakened by the /ram-alkynyl group in the bis-acetylide... 

LcU ge amplitude vibrational motions of molecules occur at high temperatures, in weakly bound complexes, in chemical reactions, and in many other circumstances. In a subset of these cases the specific (juantuni states and dynamics are important, e.g. light atom transfer reactions, unimolecular decay and isomerization of small molecules, proton transfer in liquids, photodissociation and reactions guided by laser control. 

Quasi-statistical complexes in chemical reactions have been discussed by George and Ross (1972). Depending on the extent of statistical averaging, they proposed a classification of experimental results into the categories direct interaction, doorway states (a concept borrowed from nuclear physics), partial statistical complex and complete statistical complex. They stressed that symmetric product angular distributions are indicative of complex formation, but these are neither necessary nor sufficient evidence rather, they indicated that the observations necessary for a complete statistical complex are symmetric angular distributions velocity spectrum peaked near the centre-of-mass velocity and statistical isotope distribution. 

Molecular beams provide one of the few methods for assessing the importance of stable collision complexes in chemical reactions. 

Eyring H (1935a) The activated complex in chemical reactions. J Chem Phys 3 107-120 Eyring, H (1935b) The activated complex and the absolute rate of chemical reactions. Chem Rev 17 65-82 Farman JC, Gardiner BG, Shanklin JD (1985) Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction. Nature 315 207-210... 

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