tradução de determination of mixing quantities

Experimental Determination of Mixing Quantities

∆Vmis is easily found from density measurements on the solution and the pure components or from direct measurement of the volume change on isothermal mixing of the components. ∆Hmis at constant T and P is easily measured in a constant-pressure calorimeter.
How do we get ∆Gmis? ∆Gmis is calculated from vapor-pressure measurements. One measures the partial pressures PA and PB of A and B in the vapor in equilibrium with the solution and measures the vapor pressures P°A and P°B of pure A and pure B at the temperature of the solution. The hypothetical isothermal path of fig.9.6 starts with the pure liquids A and B at T and P and ends with the liquid solution at T and P. Therefore ∆G for this six-step process equals ∆Gmis. One uses thermodynamic relations to express ∆G of each step in terms of PA, PB, P°A and P°B, thereby obtaining ∆Gmis in terms of these vapor pressures. If gases A and B are assumed ideal and the slight changes in G in steps 1 and 6 are neglected, the result is (prob. 9.62)
∆Gmis = nART ln(PA/P°A) + nBRT ln(PB/P°B)
∆Smis is found from ∆Gmis and ∆Hmis using ∆Gmis = ∆Hmis – T∆Smis.

Figure 9.6
Six-step isothermal process to convert pure liquids A and B at pressure P to a solution of A + B at P. P°A and P°B are the vapor pressures of pure A and pure B, and PA and PB are the partial vapor pressures of solution of A + B.
DETERMINATION OF PARTIAL MOLAR QUANTITIES

Partial Molar Volumes

A method for finding partial molar volumes in a two-component solution that is more accurate than the slope method of fig. 9.3 in sec. 9.2 is the following. Let n = nA + nB be the total number of moles in the solution. One plots [where ∆Vmis is defined by (9.17)] against the B mole fraction xB. One draws the tangent line to the curve at some particular composition (see fig. 9.7). The intercept of this tangent line with the axis (at xB = 0 and xA = 1) gives at the composition; the intersection of this tangent