In a typical plasma tool, both etch and deposition occur simultaneously. Extensive experimental measurements are used to help develop a general model of etch and deposition processes. This model employs reaction probabilities, or surface averaged cross sections, to link the measurable surface processes, etch and deposition, to the flux of various species to the surfaces. Because the cross sections are quantum mechanical in nature, this surface rate model should be applicable to many low temperature plasma processing systems. Further, the parameters that might be important in reaction cross sections are known from quantum mechanics, e.g., species, energy, temperature, and impact angle. Such parameters might vary from system to system, causing the wide processing variability observed in plasma tools. Finally the model is used to compare measurements of ion flux, ion energy, and fluorocarbon radical flux to the measured process rates. It is found that the model appears to be consistent with calculations of gain/loss rates for the various radicals present in the discharge as well as measured etch and deposition rates.