PHYSICAL CHEMISTRY IN BRIEF

CHAP. 6: THERMODYNAMICS OF HOMOGENEOUS MIXTURES [CONTENTS] 143

6.2 Integral quantities.

The assumption of an ideal mixture (6.1) does not apply to most common mixtures. Conse-
quently, we use mixing, excess or solution (differential or integral) quantities to describe changes
in thermodynamic quantities during mixing.

6.2.1 Mixing quantities

A change in the molar thermodynamic quantityYm, which accompanies the formation of a
mixture from pure substances in the same phase at constant temperature and pressure, is
termed themolar mixing quantity

∆YM=Ym−

∑k

i=1

xiYm•,i. (6.18)

For an ideal mixture [see6.1] we get

∆VM = 0, (6.19)

∆HM = 0, (6.20)

∆UM = 0, (6.21)

∆CVM = 0, (6.22)

∆CpM = 0, (6.23)

∆SM = −R

∑k

i=1

xilnxi, (6.24)

∆GM = RT

∑k

i=1

xilnxi, (6.25)

∆FM = RT

∑k

i=1

xilnxi. (6.26)