Why is the gaseous state called the state of greatest potential energy?
When a substance is in the gaseous state the molecules are free to move around. This creates additional pressure (ie in addition to the pressure created by the substance's weight) and increases volume. Pressure x volume = energy [(Force/distance^2)*/distance^3 = force x distance = work]. This energy can be used to do work [itex]P\Delta V[/itex]. So the gas contains PV potential energy. The liquid/solid have much lower pressure and much smaller volume so they have less PV potential energy.
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