Methods of Dealing with Equilibria

One method of obtaining equilibrium concentrations of the various species involves no simplifying assumptions. In this method as many independent equations relating the unknown quantities are obtained as there are unknowns, in which a mathematical statement for each concentration and a mathematical equation for each equilibrium reaction can be written. These are then solved. For complex systems the calculations may be cumbersome. Sillen developed a computer program HALTAFALL (available in FORTRAN) by which equilibrium concentrations of species can be calculated thout simplifying assumptions. Precise values of equilibrium constants and activity coefficients are required for best results. 

A third approach, the one we emphasize, involves the use of judgment or chemical intuition to introduce simplifying approximations at early stages in the equilibrium calculationiS. Our aim is to make the operating principles clear and unambiguous without introducing significant error. Thus, equilibrium calculations are not treated simply as mechanical operations. In most practical cases a simple equation 

FIGURE 3-1 Logarithmic diagram for 10 M acetic acid (pK, = 4.7). The system point is denoted by . 

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