Caption: In classical physics, absolute zero for a gas is reached when all the kinetic energy has been removed from the molecules or atoms in the case of a monatomic gas.

HOWSOEVER, quantum mechanics dictates that there is an irremovable miminum amount of kinetic energy called the zero-point energy.

So in our modern understanding, absolute zero for a gas is reached when you reach the zero-point energy for the molecules or atoms in the case of a monatomic gas.

Credit/Permission: © David Jeffery, 2003 / Own work.
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