- #1

- 128

- 2

In a isochoric process ##\Delta U= Q## but before to write this I need to find ##\Delta U##, which is not ##\Delta U= n c_v \Delta T## because ##c_v## is not constant.

I would calculate it with the integral

$$\Delta U= \int dU= \int_{T_A}^{T_B} n f(T) dT$$

But this assumes that ##dU## can be written and integrated, which means that the temperature is defined in any intermediate step of the process, which is in contrast with the fact that the process is irreversible.

On the other hand I don't see another way to calculate the change in internal energy in such cases, so is this method correct? If it is not, then which is the correct method to get ##\Delta U## when ##c_v=f(T)## and the process is not reversible?