Molar specific heat capacities for gases

Thread starter saubhik
Start date May 20, 2010
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Gases Heat Heat capacities Specific Specific heat

AI Thread Summary

In an isochoric process, the volume remains constant, resulting in no work done (dW=0) and thus dQ equals the change in internal energy (dU). The discussion highlights a confusion regarding the relationship between heat capacities, where it suggests that Cp equals Cv, despite the known difference (Cp - Cv = R). It emphasizes that during constant volume heating, the heat added (dQ) should relate to the internal energy change using Cv, leading to the equation Q = nCvΔT. The apparent contradiction arises from misunderstanding the definitions and applications of Cp and Cv in different thermodynamic processes. Clarifying these concepts is essential for accurate thermodynamic calculations.

May 20, 2010

saubhik

For an isochoric process,
dV = 0
therefore dW=0
So from 1st of Thermodynamics,
dQ = dU + 0
or, n*Cp*dT = n*Cv*dT (Cp and Cv denote molar heat capacities of the gas at const pressure and volume resp.)

therefore we get Cp = Cv .(how can this be possible once we know Cp - Cv = R ?)

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May 20, 2010

rock.freak667

Homework Helper

If you are heating at constant volume, how does dQ=nc_pdT?

If dQ=dU

and dU/dT = c_v, then you'll just get Q= nc_vΔT

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