Vapor pressure curve for carbon dioxide

[Sirluke]

Hello to everyone.

I would like to ask a question: I'm analyzing the properties of CO2 for a project and I have noticed that for temperatures between 220 -300 K the Clasius Clapeyron curve is linear on 1/T, that is in the Antoine equation of the form logP = A-B/(T+C), C is almost 0. In my report I stated that this is due to the fact that the heat of evaporation can be considered indipendent from temperature, but my professor answered me that this assumption is not justified and I have to look for another reason, but what's this reason? Thank you very much

 

[Bystander]

heat of evaporation can be considered indipendent from temperature

Coincidence. It's not any sort of general principle that you can apply. What else is going on that might contribute to such a numerical coincidence?

 

[Chestermiller]

The Clausius Clapeyron equation is based on the assumptions that the vapor obeys the ideal gas law, and that the molar volume of the liquid is negligible compared to the molar volume of the vapor. Maybe these assumptions are what your professor had in mind.

Chet