@context(mw=0) biogeochemistry = bgc
    # mw is the molecular weight of the species
    # volume is the volume of the solution
    # solvent_mass is the mass of solvent in the solution

    # moles -> mass require the molecular weight
    # rate = [substance] / [time]
    [substance] / [time] -> [mass] / [time]: value * mw
    [mass] / [time] -> [substance] / [time] : value / mw
@end
