Question

derive relationship between Cp&Cv. Cp-Cv=R
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Answer 1

When gas is heated through 1oC at constant pressure, the difference between these will give the work done by one mole of the gas in expansion. The difference between molar heat capacity of a gas at constant pressure, CP and at constant volume, CV is equal to the gas constant R.

Answer 2

From the equation q = n C ∆T, we can say:

At constant pressure P, we have

qP = n CP∆T

This value is equal to the change in enthalpy, that is,

qP = n CP∆T = ∆H

Similarly, at constant volume V, we have

qV = n CV∆T

This value is equal to the change in internal energy, that is,

qV = n CV∆T = ∆U

We know that for one mole (n=1) of an ideal gas,

∆H = ∆U + ∆(pV ) = ∆U + ∆(RT) = ∆U + R ∆T

Therefore, ∆H = ∆U + R ∆T

Substituting the values of ∆H and ∆U from above in the former equation,

CP∆T = CV∆T + R ∆T

CP = CV + R

CP – CV = R

Hope this helps!!