U = q + w assumptions

[Lily Guo 1D]

Does the equation (change in)U = q + w assume that there is constant pressure? Or does the pressure not have to be constant?

[Nishma Chakraborty 1J]

I don't think pressure is necessarily constant

[404995677]

On page 262 and 263, it says that work is calculated under the assumption that the external pressure is constant, so I think we assume constant pressure for (change)U= q+w.

[Jeremiah Samaniego 2C]

And if external pressure is constant, you would be able to substitute q with ∆H in the equation and w with P*∆V!

[Jessica Jones 2B]

Do we use different equations for constant pressure and constant volume?

[Jessica Nunez 1I]

According to page 273, the first law of thermodynamics (delta)U = q + w mentions that the internal energy of an isolated system is constant; however, I am unsure if we can assume pressure is constant.