When the molecular-kinetic theory of wetting dynamics on ideal surfaces is applied to heterogeneous solid substrates, effective values of its specific parameters lambda and K-0 are obtained. This paper shows that application of the Blake-Haynes equation to the velocity dependence of dynamic contact angles of water on partially methylated silica yields strong dependencies of lambda(eff) and K-eff(0) On static wettability and degree of methylation. Such dependencies can be explained by the molecular-kinetic model of dewetting dynamics on smooth heterogeneous surfaces proposed in this study. Satisfactory agreement between theory and experimental data is observed below 70% methylation, but the values of lambda(eff) and K-eff(0) Obtained at more complete coverage do not follow the theoretical predictions. At this stage we speculate that this disagreement might be due to formation of a rough coating at higher concentrations of the methylating agent and longer reaction times. Such an interpretation is based on literature data from ellipsometric and AFM studies and elemental analyses of silica surfaces methylated with trimethylchlorosilane.