P delta V is significant?

[Christy Lee 2H]

Can someone explain why P delta V is insignificant when there's a reaction with constant P that involves solids and liquids? Thanks!

[joycelee1A]

I'm not sure about all the details of it, but I do know that with solids and liquids, the volume can't really change and there's no expansion work being done. Since the pressure is constant, and liquids and solids aren't compressible, the volume isn't changing either.

[Jenny Cheng 2K]

When there's a reaction at constant pressure that involves solids and liquids, a change in volume will be insignificant because V of the reactants will equal (or almost equal) V of the products. ΔV=0, so PΔV=0. Also, there is no expansion work. Thus, with constant pressure, for a reaction that involves solids and liquids, ΔU=ΔH through the First Law of Thermodynamics.
Under constant pressure with no expansion work for reactions involving solids and liquids (w=0):
ΔU = q+w = q = ΔH

[khushic 2I]

Delta H refers to the change in enthalpy of the system. Depending on if the value is positive or negative, one can understand if the system absorbed or emits heat. Delta U is the change in the internal energy of the system which is comprised of kinetic and potential energy.

[Levon_Avedian_2H]

What does Delta H vs Delta V refer too?