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## Main Question or Discussion Point

I have a question about the deduction of First Thermodynamic Law. The book that I have is written by Paul A. Tipler and Gene Mosca and it is called

The way to deduct it is given here:

@constant volume,

Qv=Cv(T2-T1)

Because W=0, E2-E1=Cv(T2-T1)

After all, Cv=d(E2-E1)/d(T2-T1)

@constant pressure,

Given that E2-E1=Qp-P(V2-V1) and Qp=Cp(T2-T1)

We have Cp(T2-T1)=(E2-E1)+P(V2-V1)

My question is what determines the internal heat in a system is defined by CvP, which can even be used in a situation in which a different condition is given.

Please help me if you know! Thank you in advance!

*Physics: For Scientists and Engineers*.The way to deduct it is given here:

@constant volume,

Qv=Cv(T2-T1)

Because W=0, E2-E1=Cv(T2-T1)

After all, Cv=d(E2-E1)/d(T2-T1)

@constant pressure,

Given that E2-E1=Qp-P(V2-V1) and Qp=Cp(T2-T1)

We have Cp(T2-T1)=(E2-E1)+P(V2-V1)

**Now, the author replaces E2-E1 with Cv(T2-T1)**, I cannot understand this because he incites something under constant volume into a formula under constant pressure.My question is what determines the internal heat in a system is defined by CvP, which can even be used in a situation in which a different condition is given.

Please help me if you know! Thank you in advance!