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[Mandal1487]

My question is whether the first law of thermodynamics when written for the system only is valid for irreversible processes.

\deltaU_sys = Q+W is derived from the basic equation of energy conservation,

\delta(Energy of system) + \delta(Enenrgy of surroundings) = 0

Here we assume for a closed system, change in Energy of Surroundings can happen only through heat and work transfer with the system.

Thus we can write, \delta(Energy of system) = Q+W

By this logic, this relation should be valid for all kinds of processes.

But example 2.7 of "Intro.toChemical Engineering Thermodynamics" seems to indicate otherwise.

Why would we consider \delta(U_surr) when we are working on a closed system. Won't \delta(Energy of surrounding) be just equal to work done on it  = P[sub] ext [\sub] * \delta V?

Attached the pics of the example for convinience.

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•  Example 2.7.PNG   383.68KB   0 downloads
•  Example 2.7_2.PNG   337.46KB   0 downloads