Iodine free energy change

The standard potential at 25 C is 1.195 volt, and so the standai d free energy change is — 6 X 23,070 X (— 1.195) cal., or 137.8 kcal. The standard free energies of formation of solid iodine and of hydrogen ions are taken as zero, and since that for liquid water is — 56.70 kcal. rnole at 25 C, it follows that... 

Miscellaneous studies include the use of 2-aminopyridine as a standard for low wave-length spectrofluorimetry, the change-transfer complexes of iodine and aminopyridine, the linear isotherm free-energies of absorption of 2-and 3-aminopyridine on alumina, rotation mobility of an amino group by dielectric relaxation and the free energies, enthalpies and entropies of protonation. ... 

The effect of cross-links in thermodynamic stability of proteins has been evaluated by R. E. Johnson and co-workers (1978). They studied the thermal transitions of native lysozyme and of a cross-link ester derivative, the oxindole alanine lysozyme obtained by iodine oxidation (Imoto and Rupley, 1973). The change in free energy of stabilization was attributed only to the entropy decrease of the unfolded chain. 

We present a preliminary study on the structural dynamics of photo-excited iodine in methanol. At early time delays after dissociation, 1 - 10 ns, the change in the diffracted intensity AS(q, t) is oscillatory and the high-q part 4 -8 A 1 is assigned to free iodine atoms. At later times, 10-100 ns, expansive motion is seen in the bulk liquid. The expansion is driven by energy released from the recombination of iodine atoms. The AS(q, t) curves between 0.1 and 5 (is coincide with the temperature differential dS/dT for static methanol with a temperature rise of 2.5 K. However, this temperature is five times greater than the temperature deduced from the energy of dissociated atoms at 1 ns. The discrepancy is ascribed to a short-lived state that recombines on the sub-nanosecond time scale. 

If one looks at the average bond dissociation energies for X2, C-X, H-X, and C-H bonds (Table 2.2), an average heat of reaction for the halogenation of alkanes can be calculated. The results in kcal/mol are as follows F = -101, Cl = -22, Br = -4, and I = 16. The variation in these numbers comes from a continual decrease in H-X and C-X bond strengths in the series F, Cl, Br, and I. These heats of reaction reflect a dramatic change in reactivity. Free radical fluorination is so exothermic that it occurs spontaneously and very explosively. Chlorination and bromination can be controlled and are useful reactions. Free radical iodination rarely occurs. 

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