Transformation of primary minerals into secondary minerals, disintegration of rock material into fragment or particulate composition. End result of weathering is soil. Chemical weathering alters primary minerals into more stable secondary minerals and solutes.
Reactions tend to be exothermic - spontaneous and irreversible in natural environments.
Most chemical weathering rxns involve water as reactant, catalyst or medium. Solutes removed by groundwater flow feeding streams. Of course, the surface is almost completely forested now, substantial amounts of mass is being stored in aggrading biomass after being clearcut, deposition of material is probably up due to industrial activity and we expect there may have been larger erosion rates during the Pleistocene.