2. the area of skin. If the precursor is a solid state. There are a lot of surface area touching the substance will react more quickly because of the experience. Used to determine if there are solid state, precursor.
2. The surface area If the substrate is solid. The substance has a surface area to react much faster. The tangent more Consider the case of a solid substrate.
2. Surface area where reactants are solid state. The surface contact area to react faster. Because touch each other more and more. Consider the case substrate with solid state.