版权所有：华东理工大学物理化学教研室 16 There is no experimental way of separating the product γ+ γ- into contributions from the cations and the anions. we introduce the mean activity coefficient : 21 )( = −+± γγγ ++ += ± lnγ ideal μμ RT The individual chemical potentials of the ions is −− += ± ln γ ideal μμ RT 10.2 Ion activities 2) Mean activity coefficients For a 1,1-electrolyte: ± γ
版权所有：华东理工大学物理化学教研室 16 There is no experimental way of separating the product γ+ γ- into contributions from the cations and the anions. we introduce the mean activity coefficient : 21 )( = −+± γγγ ++ += ± lnγ ideal μμ RT The individual chemical potentials of the ions is −− += ± ln γ ideal μμ RT 10.2 Ion activities 2) Mean activity coefficients For a 1,1-electrolyte: ± γ
版权所有：华东理工大学物理化学教研室 17 It can be generalized to the case of a compound MpXq that dissolves to give a solution of p cations and q anions, If introduce the mean activity coefficient The chemical potential of each ion is qp s sqp = −+± )( += 1 γγγ += ± μμ RT γ ii ln ideal 10.2 Ion activities 2) Mean activity coefficients
版权所有：华东理工大学物理化学教研室 17 It can be generalized to the case of a compound MpXq that dissolves to give a solution of p cations and q anions, If introduce the mean activity coefficient The chemical potential of each ion is qp s sqp = −+± )( += 1 γγγ += ± μμ RT γ ii ln ideal 10.2 Ion activities 2) Mean activity coefficients
版权所有：华东理工大学物理化学教研室 18 The long range and strength of the Coulombic interaction between ions means that it is likely to be primarily responsible for the departures from ideality in ionic solutions and to dominate all the other contributions to nonideality. This domination is the basis of the Debye-Huckel theory of ionic solutions. 3) The Debye-Huckel limiting law 10.2 Ion activities
版权所有：华东理工大学物理化学教研室 18 The long range and strength of the Coulombic interaction between ions means that it is likely to be primarily responsible for the departures from ideality in ionic solutions and to dominate all the other contributions to nonideality. This domination is the basis of the Debye-Huckel theory of ionic solutions. 3) The Debye-Huckel limiting law 10.2 Ion activities
版权所有：华东理工大学物理化学教研室 19 The picture underlying the Debye -Hückel theory is of a tendency for anions to be found around cations, and of cations to be found around anions. Oppositely charged ions attract one another. As a result, anions are more likely to be found near cations in solution, and vice versa. Overall the solution is electrically neutral but near any given ion there is an excess of counter-ions. Averaged over time, counter-ions are more likely to be found near any given ion. This time-averaged, spherical haze, is called its ionic atmosphere. 10.2 Ion activities
版权所有：华东理工大学物理化学教研室 19 The picture underlying the Debye -Hückel theory is of a tendency for anions to be found around cations, and of cations to be found around anions. Oppositely charged ions attract one another. As a result, anions are more likely to be found near cations in solution, and vice versa. Overall the solution is electrically neutral but near any given ion there is an excess of counter-ions. Averaged over time, counter-ions are more likely to be found near any given ion. This time-averaged, spherical haze, is called its ionic atmosphere. 10.2 Ion activities
版权所有：华东理工大学物理化学教研室 20 The energy, and therefore the chemical potential, of any given central ion is lowered as a result of its electrostatic interaction with its atmosphere. This lowering of energy appears as the difference between the molar Gibbs energy Gm and the ideal value of the solute, and hence can be identified with . ideal Gm ± sRT lnγ 3) The Debye-Huckel limiting law The model leads to the result that at very low concentrations, the activity coefficient can be calculated from the Debye-Huckel limiting law 10.2 Ion activities
版权所有：华东理工大学物理化学教研室 20 The energy, and therefore the chemical potential, of any given central ion is lowered as a result of its electrostatic interaction with its atmosphere. This lowering of energy appears as the difference between the molar Gibbs energy Gm and the ideal value of the solute, and hence can be identified with . ideal Gm ± sRT lnγ 3) The Debye-Huckel limiting law The model leads to the result that at very low concentrations, the activity coefficient can be calculated from the Debye-Huckel limiting law 10.2 Ion activities