
99Reviews of Thermodynamics
formed from the basic element substances are then estimated on the basis of
the element substances and their variation from the reference state.
The Gibbs free energy of formation per unit mass is given as
g
f
= h
f
− Ts
f
on mass basis (3.102a)
and
ghTs
ff f
=− on molar basis. (3.102b)
The Gibbs free energy of formation ΔG
f
or g
f
, which is dened as the
difference in the Gibbs free energy of the product and the reactants, is
given as
ΔG
f
= Gibbs free energy of formation = (G
f
)
products
− (G
f
)
reactants
(3.103a)
∆
∆∆
GGG
ng ng
Gngg
ff
P
f
R
pfp
p
RfR
R
fPf
P
p
=−
=−
=+
()
−
∑∑
∑
0
nng g
Rf
R
R
0
+
∑
∆
(3.103b)
Note that if both the reactants a ...