Sublimation of iodine

A similar argument can be applied to the equilibrium involved in the sublimation of iodine ... 

Worked Example 4.2 By inspection alone, decide whether the sublimation of iodine (Equation (4.3)) will occur spontaneously or not ... 

The enthalpy of this process can be accurately calculated from literature data. The standard enthalpy of sublimation of iodine is known at 298.15 K (62.42 0.08 kJ mol-1 [58]), so we have (see section 2.4) ... 

Figure 9.6 A sketch of a calibration thermogram (sublimation of iodine).

If the spots on the chromatogram are faded, we can visualize them by exposing the chromatogram to iodine vapor. Place your chromatogram into a wide-mouthed jar containing a few iodine crystals. Cap the jar and warm it slightly on a hot plate to enhance the sublimation of iodine. The iodine vapor will interact with the faded... 

Solids also are pure substances with unchanging concentrations, so equilibria involving solids can be simplified in the same way. For example, recall the experiment involving the sublimation of iodine crystals in Figure 18-4 on page 562. 

Br2(f) Bt2(g) (left) and the sublimation of iodine, l2(s) 12(g) (right) both lead to an increase in disorder, so A5j,yj, > 0 for each process. Which do you think results in the more positive AS Carry out the calculation using values from Appendix K to check whether your prediction was correct. 

One of the simplest equilibria we can write is that between a solid and its vapor. Using the sublimation of iodine Ffs) — Ffe) as an example, we see that the possible equilibrium states of the system (shaded area in the diagram) are limited to those in which at least some solid is present, but that within this region, the quantity of iodine vapor is constant (as long as the temperature is unchanged.) The arrow shows the succession of states the system passes through when 0.29 mole of solid iodine is placed in a 1-L sealed container the unit slope of this line reflects the fact that each mole of I2 removed from the solid ends up in the vapor. 

State symbols are vital if thermochemical equations (see Chapter 5) are written summarising a chemical equation and its associated energy change. State symbols must be included when writing an equation summarizing a phase change (see Chapter 7), for example, the sublimation of iodine ... 

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