Further Information:

Potential Energy can be Negative!

In gases, particles are widely spaced, and the potential energy is minimal compared to the kinetic energy.

In liquids, while particles are still closely packed, they have more freedom to move, and the potential energy reflects the balance between attractive and repulsive forces as they slide past each other. Note that potential energies due to attractive forces are negative and those due to repulsive forces are positive. On average, the potential energies of particles in the liquid state are less than those in the gaseous state.

In solids, particles are closely packed and primarily vibrate around fixed positions, with potential energy largely dependent on the interatomic or intermolecular bonds. When these particles are in close proximity, the attractive forces dominate, resulting in a potential energy that is negative and lower than it would be if the particles were far apart (where the potential energy would be closer to zero or positive).

In the following simulation, you can observe the resulting potential energy as a function of the distance between two particles as a results of different types of forces (both attractive and repulsive). When particles have sufficient energy, they can overcome the intermolecular forces and leave one another.

Simulation of Potential Energy as a Function of Distance Apart