Fig. 4 Theoretical plots of dissolution rate (not normalized to surface area) vs. BET surface area. The slope of the lines connecting each data point to the origin is the apparent rate coefficient kp' (equation 14). (a) The BET surface area is linearly proportional to the reactive surface area and therefore the slope (and the obtained rate coefficient) is independent of the surface area. (b) The BET surface area is not linearly proportional to the reactive surface area and therefore the slope (and the obtained rate coefficient) varies as a function of the BET surface area.