Now, if I had billions of molecules, I would have to do it for every single molecule. Now, one last thing I want to mention is that internal energy is a state function. And what that means is simply that eternal energy does not depend on the process or the pathway taken to get to this system. What it does depend on is the current system at hand and it's also an external property. And that simply means that with increase in size of the system, internal energy of the system will also increase. And that's simply because if you increase the number of molecules in a system, there are more kinetic energies and potential energies to sum up and so that internal energy will increase.