At what state do molecules in a substance theoretically stop all movement?

The concept of molecules stopping all movement relates directly to the idea of absolute zero, which is theoretically defined as 0 Kelvin or -273.15 degrees Celsius. At this temperature, the thermal energy of the molecules is minimal, and they are thought to be in their lowest possible energy state. In this state, molecular motion ceases entirely, meaning that translational, rotational, and vibrational movements of the molecules come to a halt.

In contrast, room temperature, the freezing point, and the boiling point all represent states where molecules retain some degree of energy and thus continue to move. At room temperature, molecules exhibit a significant range of movement due to thermal energy. The freezing point is the temperature at which a substance transitions from liquid to solid; while some movement is reduced as the molecules arrange themselves in a solid structure, they do not completely stop moving. Similarly, at the boiling point, molecules in a liquid gain enough energy to overcome intermolecular forces and enter the gas phase, indicating active movement rather than a cessation of motion.

Thus, absolute zero is uniquely significant as the theoretical point at which all molecular motion is halted.