Water fugacity capacities

Fugacity capacity of gas phase Fugacity capacity of substances dissolved in water Fugacity capacity of air particles ... 

An advantage of the fugacity capacity approach is that for N compartments N values of Z are defined while there may be N(N-l)/2 partition coefficients. Using Z values the partitioning properties between two phases are attributed independently to each phase. It is possible to assign (accidentally) three inconsistent partition coefficients between air, soil and water but the three Z values are inherently consistent. 

The Level I calculation proceeds by deducing the fugacity capacities or Z values for each medium (see Table 1.5.3), following the procedures described by Mackay (2001). These working equations show the necessity of having data on molecular mass, water solubility, vapor pressure, and octanol-water partition coefficient. The fugacity f (Pa) common to all media is deduced as... 

Instead of a solid-water equilibrium relationship, a solid-air equilibrium relationship could be used in the same manner to define the fugacity capacity and the fugacity. 

The advantage of using fugacity to calculate the equilibrium distribution coefficients becomes apparent when one compares the fugacity capacities of a HOP for several different phases. For example, consider a region of the unsaturated zone just below the ground surface where naphthalene is distributed between air, water, pure phase octanol, and soil at equilibrium. The fugacity capacities for these phases are repeated below in Eqs. (46)-(49) ... 

The fugacity capacity for other phases is a function of both the chemical s partition coefficient between that phase and water and the chemical s Henry s law constant. For water, the fugacity capacity is... 

Therefore, at equilibrium, the mass of methylene chloride will be overwhelmingly in the air as compared with the other two phases. However, the highest concentration of methylene chloride is in the water (1 X ICE7 mol/m3), the phase with the highest fugacity capacity. 

The equilibrium constant is then the ratio of the fugacity capacities. The magnitude of Z will depend on temperature and the properties of the compound as they relate to the characteristics of a given phase. Compounds will accumulate in compartments with a high value of Z. The next step is to define Z for environmental compartments air, water, soil, sediments, and biota. 

The fugacity capacity in water is thus the reciprocal of the Henry s law constant. It should be emphasized that the concentration of the compound in water refers only to the amount in solution and does not include compound that could be associated with suspended sediment, for example. 

In this approach,four heterogeneous compartments are considered with the volume fractions given in Table 10.10. The fugacity capacity, Z, of each compartment is a composite value based on the Z values of each constituent. The rates of transformation in and advection from compartments are defined by the same D values outlined in the Level E model. Transfer between compartments involves a number of different processes (Table 10.11), which also are defined by D values with the same units, mol -h Pa . An overall D value for transfer between two compartment will be the sum of the D values for the individual processes involved. Transfer mechanism involves either a diffusion process similar to that responsible for the evaporation of a compound from water (see Evaporation, Chapter... 

Figure 5.17 illustrates the effect on hydrate formation when ethane and propane are combined at constant temperature. Ethane acts as an inhibitor to sll formation due to competition of ethane with propane to occupy the large cages of sll. Propane also acts as an inhibitor to si formation when added to ethane+water. In this case, however, since propane cannot enter the si cavities, the fugacity of ethane is lowered as propane is added, destabilizing the si hydrate. Holder (1976) refers to this inhibiting capacity as the antifreeze effect. 

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