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A substance changes from a solid to a liquid during the process of melting. What happens to the temperature and arrangement of the particles in the substances as it melts?

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First of all you need to understand that molecules have motion.  All molecules higher than the temperature of absolute zero (0 degrees Kelvin) move in proportion to their temperature.  In other words, hot molecules will have a higher degree of motion than cold molecules.  When a solid is heated up, its molecules will absorb that energy and increase their molecular motion.  So as the material goes from a solid to a liquid, the molecular motion increases as does the space between the molecules.  This increased space and motion is what allows a liquid to be less dense than a solid (in general) and allows it to move spontaneously to fill the space of its container.  Continued heating will allow the liquid to absorb even more energy and boil to become a gas, which is even less dense with more space between molecules and a higher degree of molecular motion than either a liquid or a solid.

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In a solid, molecules are arranged in a crystalline structure and move slowly. The closer the temperature of the substance is to zero degrees Kelvin, the slower they move. The temperature of a substance increases as energy is added and absorbed. When a substance absorbs energy, the molecules within the substance increase in movement.The absorption of energy results in an increase in charge of the electrons in the outermost orbit of the molecule. This causes a more powerful repulsion between particles. There is a corresponding increase in movement with increased space between the molecules to accommodate the greater repulsion. A substance transitions from a solid to a liquid when it absorbs enough energy to surpass its melting point. A liquid will continue to absorb energy until it reaches the phase of gas.