PHYSICAL CHEMISTRY IN BRIEF

CHAP. 6: THERMODYNAMICS OF HOMOGENEOUS MIXTURES [CONTENTS] 140

Note:We will use the terms ideal mixture and ideal solution as synonymous.

The molar thermodynamic quantities of an ideal mixture are given by the following relations:

Vm,id.mix =

∑k

i=1

xiVm•,i, (6.2)

Hm,id.mix =

∑k

i=1

xiHm•,i, (6.3)

Um,id.mix =

∑k

i=1

xiUm•,i, (6.4)

CVm,id.mix =

∑k

i=1

xiCVm• ,i, (6.5)

Cpm,id.mix =

∑k

i=1

xiCp•m,i, (6.6)

Sm,id.mix =

∑k

i=1

xiS•m,i−R

∑k

i=1

xilnxi, (6.7)

Gm,id.mix =

∑k

i=1

xiG•m,i+RT

∑k

i=1

xilnxi, (6.8)

Fm,id.mix =

∑k

i=1

xiFm•,i+RT

∑k

i=1

xilnxi. (6.9)

6.1.2 Ideal mixture of ideal gases

A special case of an ideal mixture is an ideal mixture of gases with all its components obeying
the equation of state of an ideal gas. Equation (6.2) then rearranges to

Vm=

RT

p

. (6.10)

When calculating the molar thermodynamic quantities of an ideal mixture of ideal gases,
we proceed either from the properties of the gas at the temperature and pressure of the system,