Oxidizing strength of the halogens in aqueous solution

As noted earlier, the relative oxidizing strengths of the elemental halogens are given by the values of ( X21 X ) in Table 6.1 they run in the order F2 CI2 Br2 l2-Here we shall only outline the conclusions of a thermodynamic analysis of this trend. 

When the elemental halogens act as oxidizing agents, they are converted into X (aq) ions. In the process, we imagine first a step in which X2 is converted into X (g). The energy of this step is most favourable for fluorine, but it is quite similar for all the halogens the values of AH (X , g) in Table 6.4 illustrate the point. 

There is then a step in which the gaseous halide ions are immersed in water X-(g) = X-(aq) 

So in passing from X2 to X (aq), there is an intermediate step from X2 to X (g), whose energy is similar for all the halogens then there is a subsequent step from X (g) to X (aq), which becomes much less favourable from fluorine to iodine. 

It makes the ease with which 2X2 is converted to X (aq) diminish that is, it causes a decrease in the oxidizing strength of X2. 

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Self-Test 15.5A Predict the trend in oxidizing strength of the halogens in aqueous solution. 

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