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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.

valerio
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J.Jones
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    Your book is wrong: even at absolute zero the kinetic energy of the molecules is not zero, because this would violate Heisenberg's uncertainty relation. Take a look here: https://physics.stackexchange.com/questions/56170/absolute-zero-and-heisenberg-uncertainty-principle – valerio Jun 03 '17 at 14:28
  • Depending on the level, the book's decision to go with "it's all stopped at absolute zero" may well represent a conscious decision to use a lie-to-children. Student who are just ready for the notion of absolute zero are probably not ready for HUP, so that detail gets left out by design. – dmckee --- ex-moderator kitten Jun 03 '17 at 15:10
  • @dmckee♦ I thought the same thing, this is only an A-level textbook, however, I I try not to jump to such conclusions without asking around. Thank you for your contribution. – J.Jones Jun 03 '17 at 15:17
  • Asking about such things here is fine. Because books do that and people then approach them with differing levels of preparation a certain amount of confusion on the part of better prepared readers is perfectly normal and a question on the site which resolves it is a good thing. – dmckee --- ex-moderator kitten Jun 03 '17 at 15:20

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