This is a topic which thoroughly confuses me, I've read in my textbook that:
Absolute zero is the lowest temperature possible. At this temperature, the internal energy is a minimum. The kinetic energy of all molecules is zero.
So far this makes logical sense to me, however, the textbook goes on to say:
The internal energy is not zero because the substance still has electrostatic potential energy stored between the particles.
For me, this is the confusing part because electrostatic potential energy is negative. So surely at absolute zero, the internal energy would be negative. I then asked myself whether the internal energy is always negative and came to the conclusion that that cannot be the case. For instance, a gas would (I think) have positive internal energy, due to negligible potential energy and kinetic energy would be positive.
I've looked around and unfortunately, I can only seem to find articles about the change of internal energy being zero. Admittedly, for the course I'm studying this is as in depth as it gets regarding thermodynamics, so I don't really have any knowledge of entropy / other things related to thermodynamics.
