Physical Chemistry of Foods

smaller for phasebthan for phasea. This is illustrated in Figure 14.1a.

Remembering thatG¼H
TDS, we derive that

DtrG¼GðbÞ
GðaÞ¼DtrH
TDtrS ð 14 : 1 Þ

Since atT¼Teqwe haveDtrG¼0, it follows that

DtrH¼TeqDtrS ð 14 : 2 Þ

Combination of (14.1) and (14.2) now gives

DtrG¼DtrH 1 

T

Teq



¼DtrSðTeq
TÞð 14 : 3 Þ

FIGURE14.1 (a) Free energyGof a material when present in two different phases,
aandb, as a function of temperatureT; the broken lines are extrapolations beyond
the temperatureTeqat which both phases are in equilibrium. (b) The change in free
energyDtrGupon transition fromatobas a function of temperature. Highly
schematic.