And the formula is this the change in enthalpy is equal to change in U plus P times change in B. So let's see what this guy is. This guy is just a total internal energy of the system, okay? And if you look at this system here, which is a circle or a sphere, it's basically the collective energy of all the different molecules found within the system. So you sum their kinetic energies and you sum their potential energies, and that gives you, this guy here, the total infernal energy of the system. What this is is it's the work done to displace environment in creating the current state of the system, okay?