Utotal

[Hailey Boehm 2H]

What is the significance of utot= (3/2)NRT for an ideal gas and reversible expansion? When would I know to us this/ when does it apply?

[ian_haliburton_1f]

This comes from the fact that we're treating the gas as only being able to move in 3 directions. Its molecules can move in any direction x, y or z, so we write 3/2. We ignore the possibility that it has rotational or vibrational energy, which would make this coefficient higher. Dr. Lavelle just brought this up as another way to show that since utot= (3/2)NRT, ∆U=3/2nR∆T, and that in reversible isothermal expansion ∆T is 0, so ∆U is 0 overall as well.