SiO2 + 2C     = 2CO + Si(l)       (1)

Si(l)
=   Si                   (2)

____________________________

SiO2 + 2C = 2CO + Si             (3)

where fSi is the activity coefficient for the 1
wt % ss.

The value of fSi is always close to unity since
dilute solutions depart little from infinite dilution behavior.  It is recommended not to exceed a
percent, or 2 at most.

Note the similarity of f with gamma

The ideal lines always run through (0,0) to (1,1)