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## gorica 2 years ago Do you know where can I find how to get relations between heat capacities Cp and Cv for ideal and real gases? Or someone can write it here?

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1. LvL-Whitey

You can always start with Cv=3/2R for a monatomic particle and use Cp=Cv+R. Cv= 5/2R for Diatomic CV= 3R for Polyatomic R is a constant that you know right? Cheers :D

2. gorica

I have to show why is it Cp=Cv+nR for ideal gas and why it is what it is for real gas. I found this, and I am ok with ideal gas... but I am not really clear with real gas :/

3. LvL-Whitey

OooOOooo, That complicates things then :( I'm not sure I can help you further, sorry Cheers :D

4. gorica

thanks anyway :)

5. ghazi

hope this will help you out , hold a sec

6. ghazi

if you are not able to read it , let me know :)

7. gorica

I think I found what I was looking for... via coefficient of volume expansion Thank you very much

8. ghazi

$h= u+PV$$dh=du+d(PV)$ $dh=du+d(RT), dh=du+RdT$$\frac{ dh }{ dT }=\frac{ du }{ dT }+R$$C _{p}=C _{v}+R, C _{p}-C _{v}=R$ you can use this derivation too

9. ghazi

and you are welcome :)

10. gorica

what is h?

11. ghazi

h-- enthalpy u -- internal energy dh/dT -- Cp du/dT-- Cv

12. gorica

is Cp defines as dh/dT or we get it somehow because p=const?

13. gorica

*defined

14. ghazi

yep, Cp is specific heat capacity at constant pressure, and change in enthalpy at with temperature is the same quantity , for ideal gas dh=CpdT and gamma = Cp/Cv

15. gorica

ok. I will read this all again and if I have more questions, I will write them tomorrow, ok? :) thank you again :)

16. ghazi

sure :)

17. gorica

do you maybe have graphs of isotherms of Van der Waals gas and real isotherms and something about thermometer with thermocouple, I can't find it on internet?

18. ghazi
19. ghazi
20. gorica

:) thanks :)

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