PHYSICAL CHEMISTRY IN BRIEF

CHAP. 6: THERMODYNAMICS OF HOMOGENEOUS MIXTURES [CONTENTS] 159

• For a real mixture we have
  fi=φixip , (6.81)
  whereφiis the fugacity coefficient [see6.5.2]

6.5.2 Fugacity coefficient

Thefugacity coefficient[see3.2.7] of theithcomponent in a mixture is defined by the relation

φi=

fi

p xi

. (6.82)

U Main unit:dimensionless quantity.

• Thedependence of the fugacity coefficient on temperatureis expressed by the
  relation
  lnφi(T 2 ) = lnφi(T 1 ) +

∫T 2

T 1

(

∂lnφi

∂T

)

p,n

dT , (6.83)

where (

∂lnφi

∂T

)

p,n

= −

Hi−Hm◦,i

RT^2

. (6.84)

• Thedependence of the fugacity coefficient on pressureis expressed by the relation

lnφi(p 2 ) = lnφi(p 1 ) +

∫p 2

p 1

(

∂lnφi

∂p

)

T,n

dp , (6.85)

where (

∂lnφi

∂p

)

T,n

=

Vi

RT

−

1

p

. (6.86)

• In the case of anideal mixture[see6.1], theLewis-Randall ruleapplies

φi=φ•i, (6.87)

i.e. the fugacity coefficient does not depend on composition but only on temperature

and pressure. For an ideal mixture of ideal gases [see6.1.2] we than have

φi= 1. (6.88)