# Molar heat capacity of constant volume for an ideal gas under constant pressure?

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

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.

• When i did ratio of heat capacities however i get a value of 2.6 so does that mean its diatomic ? – WDUK Mar 21 '19 at 7:09
• @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. – reversiblecycle Mar 24 '19 at 8:01