How do we explain physical changes in terms of the arrangement and motion of atoms and molecules?

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A physical change could be done in a variety of ways, but one simple and common physical change is melting and freezing. When a substance is a solid, the arrangement of its atoms and molecules is tight and organized. The particles are not capable of sliding over and past each other or flying away from each other as they do in gasses. When you melt a substance, you are more than likely adding thermal energy to it. As the solid absorbs this thermal energy, the molecules begin vibrating more and moving farther and farther apart from one another. Their arrangement gets looser and looser until they are free enough to begin sliding past each other. The substance is now a liquid. Freezing reverses the process, and the molecules become less energetic and more organized as the substance returns to being a solid. In summary a physical change causes the motion of the particles in the substance to change as well as the distance between the particles.

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