[shafaifer]

This exercise is about calculating the standard molar entropy for the phase change l  :rarrow:g. I need a hint for this exercise. I am not sure if it is necessary to include all of the seven given conditions in order to calculate the standard molar entropy for CH₃OH(g). I have searched on this topic without progress. Is there something very basic I have not seen?

With best regards,

Shafaifer

[mjc123]

Yes, you need all the information because of the temperature dependence of S.
At T_vap you know ΔG_vap = 0 = ΔH - TΔS, so you know ΔS_vap at T_vap.
The temperature dependence of S is given by dS/dT = C_p/T
So you set up a Hess's law cycle, with the following steps:
1. Heat CH₃OH (l) from 298K to T_vap; ΔS1
2. Vaporise CH₃OH(l) at T_vap; ΔS2
3. Cool CH₃OH(g) from T_vap to 298K; ΔS3
The overall entropy change ΔS1 + ΔS2 + ΔS3 is the entropy difference between vapour and liquid at 298K.

[shafaifer]

Thank you very much.