Page 155 - Chemical equilibria Volume 4

Determination of the Values Associated with Reactions – Equilibrium Calculations 131
“OC”. If these two arrangements are practically equivalent in terms of
energy, this means that the number of complexions at absolute zero for a set
N
of N molecules (n moles) will be Ω= 2 , and thus the residual entropy of
CO will be:
N
0
s = k ln2 = N k ln2 = n R ln2 [4.39]
B
0
B
Generally speaking, if s represents the number of equivalent
configurations at absolute zero, the molar residual entropy will be:
s = Rln s [4.40]
0
0
The last column in Table 4.5 shows the values calculated for a number of
molecules, and we see a very close correspondence with the observed values,
shown in the fourth column.

NOTE 4.5.– Up until now, we have defined an entropy known as the absolute
entropy, because it is characterized by a number of complexions equal to 1.
In fact, in that number, we have only taken account of the states of the
nucleus, the electrons and the atoms. There is nothing to suggest that, were
we to take account of the states of the particles internal to the nucleus such
as protons, neutrons or other nuclear subatomic particles, we would actually
obtain the same “absolute” entropy. In fact, our absolute entropy can be
qualified as chemical: strictly speaking, it remains a relative entropy value:
that calculated by taking the number of complexions at the scale of the atom
as equal to 1.

4.4. Specific heat capacities

The values of the specific heat capacities are found by two different kinds
of experimental methods: calorimetric methods and spectroscopic
techniques.

4.4.1. Calorimetric measurements of the specific heat capacities

Specific heat capacities found by calorimetry are usually represented as a
function of the temperature, by functions in the form:

a bT +
C =+ cT + dT − 2 [4.41]
2
P