chemical equilibria and kinetics in soils

[...]... Tl'nxth; 10 CHEMICAL EQUlLmRIA AND KINETICS IN SOILS (1.17) where Zi is the valence of the metal or ligand whose total molality is m Ti and the sum is over all metals (including hydrogen) and ligands (including hydroxide) in solution The Debye-Hiickellimit for the single-ion activity coefficients of an electrolyte is similar to Eq 1.16: (1.18) where I.,f is the effective ionic strength: (1.19) In Eq 1.19,... opposite charge At finite ionic strength, Young's rules suggest that any mathematical expression for In 'Y ± (or In 'YM and In 'YL) should include both linear and bilinear terms in the molalities of all metals and ligands (or all charged species) in an aqueous solution 10 The Davies equation is a semiempirical expression for calculating single-ion activity coefficients in soil solutions having effective... applied to the reaction in Eq 1.3, since it does not display the actual molecular mechanism involving the intermediate species, H2 COg, OH-, and Hp Therefore, it would be incorrect to interpret the reaction in Eq 1.3 as the combination of one CO2 molecule with a water molecule to form H' and HCO;- ions The error in this line of reasoning is brought into sharper focus after noting that the elementary... exclusively in the gaseous phase or the solid matrix of soilless often control its chemical behavior than reactions involving the aqueous phase The basic terminology associated with the latter chemical reactions will be reviewed in the present chapter to provide an initial context for the discussion of equilibria and kinetics to follow A chemical reaction is termed elementary if it occurs in a single step,... species in the solution In the limit of infinite dilution, soluble complexes should make a negligible contribution to lef' If this is true, then Eqs 1.16 and 1.18 can be combined into the following single equation: Lim _1_ Ierl-0 a + b In[ Y~Y~l = Lim In I,~O Y± (1.20) This equation represents a general theoretical constraint on single-ion activity coefficients A general empirical constraint on single-ion... Reactions in Soils Soils are multicomponent, multiphase, open systems that sustain a myriad of interconnected chemical reactions, including those involving the soil biota The multiphase nature of soil derives from its being a porous material whose void spaces contain air and aqueous solution The solid matrix (which itself is multiphase), soil air, and soil solution-each is a mixture of reactive chemical. .. sequential reaction in Eq 1.52 is (1.54a) CHEMICAL EQUILffiRIUM AND KINETICS 21 (1.54b) (1.54c) Because of the stoichiometric constraints implied by Eqs 1.51 and 1.52, not all the rate equations in Eqs 1.53 and 1.54 are independent In Eq 1.53, the rate at which the concentration of species C increases must be the same as the combined rates of decrease in the concentrations of species A and E, such that... matter and energy to and from the vicinal atmosphere, biosphere, and hydrosphere These external flows, as well as the chemical composition of soil, vary in both space and time over a broad range of scales The complexity of soil notwithstanding, the principal features of its chemical behavior can be understood on the basis of well-established principles and methods for the description of reactions in aqueous... change In the limit of infinite dilution, these interactions must die out, and the extrapolated value of Kc must represent chemical equilibrium in an ideal solution wherein species interactions (other than those involved to form a complex like HC0:J) are unimportant The concentrations in Kc become equal numerically to activities in the limit of either no interactions among species (Infinite Dilution Reference... reactants and products in their Standard States: CHEMICAL EQUILmRIUM AND KINETICS ~ r GO = -RT In K 17 (s1.14) where ~,G0 is the standard Gibbs energy change, R is the molar gas constant, and T is absolute temperature The conceptual meaning and numerical calculation of ~rGo are discussed in Special Topic 1 Suffice it to say here that ~rGo can be expressed formally as the algebraic sum of two other Standard-State .