Iodine potential diagram

The chemical potential diagram for this ternaty system (Figure 3.3) shows that the reaction with the elements would reduce the iodine pressure to a very low value, which is not suitable for CVD, whereas tire compound Ta5Si3, in which the chemical potentials of the two elements are about 40kJgram-atom would be suitable for CVD at about 1300 K. 

Fig. 17.14 Potential diagrams for chlorine, bromine and iodine at pH = 0. A Frost-Ebsworth diagram for chlorine (pH=0) is given in Figure 17.15 in problem 17.21 at the end of the chaper.

Several of the alpha-ethyl analogues of ARIADNE were N,N-dialky lated, and were target compounds for halogenation with radio-iodine or radio-fluorine, for evaluation as potential brain blood-flow indicators. In these studies, all examples followed a common flow diagram. The reaction of the appropriate benzaldehyde... 

Potential-energy diagram for molecular iodine. The energy zero has been arbitrarily set at the minimum of the ground-state potential. 

FIGURE 21.29 Potential-pH equilibrium diagram for the iodine-water system at 25 °C, for solutions containing Ig-at I/l (from Ref. 41). 

Potential-pH diagrams are often convenient as an aid in predicting the direction and course of redox reactions. If two such diagrams are superimposed, the system of higher potential at any pH will act as an oxidant. If the lines of two systems intersect, the direction of reaction may be reversed by a change in pH. As an example, a comparison of the iodine-iodide and As(V)-As(III) tems (Section 19-5) shows that iodine acts as an oxidant to produce As(V) at higher pH values and As(V) acts as an oxidant to produce iodine at low pH values. 

To illustrate the use of these diagrams, the stability of I2 in 1 Af base will be considered. The diagram for iodine-containing species in base shows I2 will disproportionate to 1 and IO [Eq. (15)]. IO should, however, also be unstable, undergoing disproportionation to 1 and lO [Eq. (16)]. Eurther disproportionation of lOj is not expected because the reduction potential involving formation of IO4 is more positive than any reduction potential to the left of 10. It should be noted that these diagrams only predict what reactions are allowed to happen they say nothing about how fast the reactions will occur (see Section I.G.). 

Sketch the potential energy profile for the reaction between propanone and iodine. Simplify the diagram by combining the fast stages into one combined second stage. 

Figure 3-8 Potential-energy diagrams (left) the reaction of a fluorine atom with CH4, an exothermic process with an early transition state and (right) the reaction of an iodine atom with CH4, an endothermic transformation with a late transition state. Both are thus in accord with the Hammond postulate.

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