Page 134 - Chemical equilibria Volume 4

110 Chemical Equilibria
This gives us the expression:
Δ h = 11858 0.065T
−
0
v T
Similarly, the standard entropy at T will be given by:
1357 C (s ) T Δ C
ol
F 1357 ∫
Δ v T 0 Δ s = v 298 ∫ s 0 + P dT + Δ s + v dT
298 T 1357 T P
By feeding the values of the specific heat capacities into this equation, we
find:

1357 ( 0.111 3.52.10 T− − − 3 ) 741.6 T 0.605
Δ v T 0 Δ s = v 298 ∫ s 0 + dT + − ∫ dT
298 T 1357 1357 T
This expression can be simplified to:

0
Δ s = 761 0.605 lnT
−
v T
Ultimately, the standard Gibbs energy is:
s =
−
T
Δ v 0 T Δ g = v T 0 T Δh − v T 0 11858 760.9T + 0.605 lnT
This gives us a value for the saturating vapor pressure, expressed in bars,
which is the equilibrium constant of the vaporization reaction:

+
v
ln P (vap ) = ln K (I) = − Δ g T 0 = − 91.45 0.072lnT − 1425
Cu
RT T
As we can see, the expressions with which we are working here can
quickly become rather complex, which is why it is so helpful to use
computer technology to perform the calculations.

4.2. Enthalpies of reaction – thermochemistry

We know that the reaction enthalpy is identical to the reaction heat at
constant pressure. The properties and means of determining these reaction
heats make up hermochemistry.