Internal energy change in isobaric system

AI Thread Summary
In an isobaric system, the first law of thermodynamics states that ΔQ = ΔU + W, where W is the work done by the system. For isobaric processes, work can be expressed as W = PΔV, allowing for the calculation of heat transfer ΔQ. The change in internal energy ΔU for an ideal gas is directly related to the change in temperature ΔT, and can be expressed using specific heat capacity at constant volume (Cv). The specific heat capacity at constant pressure (Cp) is also related to ΔU, as Cp = Cv + R for ideal gases, linking changes in internal energy and temperature. Understanding these relationships is crucial for analyzing energy changes in thermodynamic processes.
cooper607
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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?
please help
 
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cooper607 said:
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?
please help
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
 
well as for ideal gas U is only function of T, so i think we can replace dU with dT...but i just don't 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?
 
cooper607 said:
well as for ideal gas U is only function of T, so i think we can replace dU with dT...but i just don't 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?
What is the relationship between ΔU and ΔT (for an ideal gas? What is the relationship between Cv and Cp?

AM
 
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