PHYSICAL CHEMISTRY IN BRIEF

CHAP. 6: THERMODYNAMICS OF HOMOGENEOUS MIXTURES [CONTENTS] 163

0 mst cst x 1 1

H 1 [m]

H 1 [c]

H 1

H 1 [x]

H 1 •

Obr.6.3:Definition of the standard states for component 1 in a binary mixture. The curve ending
at pointH• 1 represents the dependence of partial molar enthalpy on composition, and the straight
line is its tangent at pointx 1 = 0. H 1 • is the standard enthalpy of a pure component. H 1 [x] is the

standard enthalpy in the standard state of a hypothetical pure component at infinite dilution,H 1 [c]is
the standard enthalpy in the state of unit molar concentration, andH 1 [m]is the standard enthalpy in
the state of unit molality.

where (

∂lnai

∂T

)

p,n

= −

Hi−Hist

RT^2

. (6.92)

• The dependence of activity on pressure is expressed by the relation

lnai(p 2 ) = lnai(p 1 ) +

∫p 2

p 1

(

∂lnai

∂p

)

T,n

dp , (6.93)

where (

∂lnai

∂p

)

T,n

=

Vi−Vist

RT

. (6.94)