Some solutes (e.g. O2(g) and saccharose C12H22O11(s)) dissolve as whole molecules in water, whereas other solutes (e.g. HCl(g) and NaCl(s)) dissolve practically fully ionised, splitting in two ions or more (CaCl2 yields 3 ions), so that the activity in the diluted limit varies with or and not with As ci2 cin ci. pure ions cannot be isolated (they always form electrically-balanced in pairs, terns or so), activities and activity coefficients cannot be measured for one ion but for the set of ions formed (e.g. etc.). aHCl(aq)=mHmCl, aCaCl2(aq)=mCam2Cl, For a system subjected to a chemical reaction 0=iMi, with the extent of reaction, , and the affinity, A, defined by (ni-ni0)/i and the Gibbs function of reaction is given by: Aii,, (18) where the effect of the pressure change from to in the liquid phase has been neglected, and the same p p symbol i* stands for pure gases, pure liquids, and infinitely-diluted solutions. Equilibrium constant The so called equilibrium constant, and activity quotient, are defined by: K(T,p), Q(ai), , and (19) so that at any state and at equilibrium (A=0): gr=RTln(K/Q), (20) The name activity 'quotient' derives from the fact that some of the stoichiometric coefficients in the Q product are negative (the product is really a quotient of products).
Some solutes (e.g. O2(g) and saccharose C12H22O11(s)) dissolve as whole molecules in water, whereas other solutes (e.g. HCl(g) and NaCl(s)) dissolve practically fully ionised, splitting in two ions or more (CaCl2 yields 3 ions), so that the activity in the diluted limit varies with ci2 or cin and not with ci. As pure ions cannot be isolated (they always form electrically-balanced in pairs, terns or so), activities and activity coefficients cannot be measured for one ion but for the set of ions formed (e.g. aHCl(aq)=mHmCl, aCaCl2(aq)=mCam2Cl, etc.). For a system subjected to a chemical reaction 0=iMi, with the extent of reaction, , and the affinity, A, defined by (ni-ni0)/i and Aii,, the Gibbs function of reaction is given by: (18) where the effect of the pressure change from p to p in the liquid phase has been neglected, and the same symbol i* stands for pure gases, pure liquids, and infinitely-diluted solutions. Equilibrium constant The so called equilibrium constant, K(T,p), and activity quotient, Q(ai), are defined by: , and (19) so that at any state gr=RTln(K/Q), and at equilibrium (A=0): (20) The name activity 'quotient' derives from the fact that some of the stoichiometric coefficients in the Q product are negative (the product is really a quotient of products).
Excess%20functions.docx