I'm a bit confused by this. For an ideal gas under pressure of n moles. If some amount of energy is added Q and the temperature increases dT how do you find Cv ?

Molar heat capacity for pressure i can find with Cp = Q/dT but i am trying to understand how to also find Cv so i can then determine if the gas is monatomic or diatomic with given values. Via the ratios Cp/Cv = 1 + 2/f

Hope some one can help explain this a bit as i've struggled to understand this topic at the moment.


1 Answer 1


If you already have Cp, then you can easily calculate Cv using the equation Cp-Cv=R, where R is the gas constant of the particular gas you are investigating.

  • $\begingroup$ When i did ratio of heat capacities however i get a value of 2.6 so does that mean its diatomic ? $\endgroup$
    – WDUK
    Mar 21, 2019 at 7:09
  • $\begingroup$ @WDUK I am from an Engineering background so I'm not too sure about this, but according to some data on web.mit.edu/16.unified/www/FALL/thermodynamics/notes/… it says the ratio of specific heat capacities should be around 1.4 for a diatomic substance around the temperatures 150-600K. $\endgroup$ Mar 24, 2019 at 8:01

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