internal energy change in isobaric system

cooper607

hi all, i have a confusion about the internal energy change and work done in a isobaric system....
suppose i want to find the delQ in isobaric system in terms of P & V....now i may assume the delW part would be pdv=p(V2-V1)...as i m compressing the gas...
but what happens to the du?
and is the specific heat capacity at const pressure somehow related to the du?
plz help

Andrew Mason

Use the first law:

ΔQ = ΔU + W where W is the work done by the system.

If the compression is slow enough, you could treat it as a quasi-static isobaric compression such that W = PΔV.

To find ΔQ all you have to do is find ΔU. If this is an ideal gas, that is easy to do because ΔU is related to ΔT (how?) and ΔT is related to Δ(PV) by the ideal gas law. Or you could just use Cp and the change in T to determine ΔQ.

AM

cooper607

well as for ideal gas U is only function of T, so i think we can replace dU with dT...but i just dont want to split the delQ here....
so i wanted to know is there any direct link between Cp and dU so that somehow i can replace the dU in terms of Cp & dT?

Andrew Mason

What is the relationship between ΔU and ΔT (for an ideal gas? What is the relationship between Cv and Cp?

AM