Reaction Constant P

[Cynthia Ulloa]

Can someone briefly re-explain what would happen to our internal energy when our P is constant and the moles of a gas change versus when our P is constant and solids and liquids are involved? I more or less understand what the Professor said at Friday's lecture, but I just want clarification.

[Jonas Talandis]

I think it's a similar concept of not including solids or liquids in equilibrium expressions. The gas is the only phase that is able to affect volumetric change. But idk lol

[Matthew Mar 1J]

The formula for internal energy is U = q+w, but when pressure is constant w = -P/\V, which gives us /\U = q - P/\V.
If there's a gas involved, we can use the ideal gas law PV = nRT to get /\U = q - /\nRT, where /\n is the change in moles. According to this equation, when moles increase, internal pressure will decrease for a system with gas under constant pressure.
Solids and liquids have a set volume so there won't be any /\V.

[Margaret Akey]

the biggest difference is that in solids and liquids there is no volume change!!