Example 3.3 Calculating the entropy at low temperatures
The molar constant-pressure heat capacity of a certain solid at 4.2 K is 0.43 J K−1
mol−1
. What is its molar entropy at that temperature?
Method Because the temperature is so low, we can assume that the heat capacity
varies with temperature as aT3
, in which case we can use eqn 3.22 to calculate the
entropy at a temperature T in terms of the entropy at T = 0 and the constant a.
When the integration is carried out, it turns out that the result can be expressed in
terms of the heat capacity at the temperature T, so the data can be used directly to
calculate the entropy.
Answer The integration required is