Entropy reaction chains

Thus the function T(x) that minimizes the entropy production P is linear in x, i.e. the entropy production is minimized when the heat current reaches a uniform value along the length of the system. This result has a formal similarity with the velocities of a sequence of coupled reactions all being constant along the reaction chain (Example 2). As expected, the stationary state obtained in the previous section using the heat conduction equation (17.1.5) is identical to (17.2.44). 

The thermal decomposition of pure HN3 at 538 to 598 K is first order with k(s" ) = 44.5X 10 exp(-130 kJ morVRT) the supposed reaction chain is not interrupted by added NO. The large entropy of activation of -109 J mor indicates a decomposition on the glass surface of the reaction vessel [11]. The decomposition of HN3 after injection into a vessel heated to 820 to 970 K follows first-order kinetics with a rate constant of k(s" ) = 10 2 exp( -172 kJ mor /RT) [21 ]. 

The standard entropy change for the atom-molecule reactions is in the range 5-20 mole and the halogen molecule dissociation has an eiiU opy change of about 105 e.u. The halogen molecule dissociation energy decreases from chlorine to iodine, but the atom-molecule reactions become more endothermic from chlorine to iodine, and this latter effect probably influences the relative contributions to the mechanism from chain reaction and biinolecular reaction. 

The data in Table 191 show a large difference in entropy of activation for reaction of the 4-methoxy compound in the three acids. The difference in the data for perchloric and sulphuric acids was again thought to arise from a significant amount of reaction in the latter occurring via bisulphate anion. This anion was proposed as being insufficiently electrophilic to react except by coordination with the side chain, as in scheme (2S0)... 

Entropy of activation is also responsible for the difficulty in closing rings larger then six membered. Consider a ring-closing reaction in which the two groups that must interact are situated on the ends of a 10-carbon chain. In order for reaction to... 

Cyclisation of polymer chains. Theory and experiment 64 Entropy changes for cyclisation reactions in solution 74... 

Fig. 5 Entropy effect on simple gas-phase cyclisation reactions. Symmetry cor rected 0 quantities plotted against the number of single bonds in the open-chain reac tants. Data from Table 5...

Given that the first approximation for solvent interactions seems adequate to a reasonable degree of accuracy, with the possible exception of some of the very short-chain compounds, we can now attempt an extension to available entropy changes for cyclisation reactions in solution of the same treatment as was applied in the preceding section to entropy changes for hypothetical cyclisation reactions in the gas phase. 

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