ABSTRACT
Plasma is a mixture of electrons, negatively and positively charged par ticles, and neutral atoms and molecules. Plasma is considered as being a state of materials, and the state is more highly activated than in the solid, liquid, or gas state. From this sense, the plasma state is frequently called the fourth state of materials. Materials composed of many atoms, mole cules, or compounds transfer from solid to liquid or gas with an increase in temperature. We consider the transition of ice to water to aqueous vapor. In ice (solid state), each of the H20 molecules is positioned at a given position in the crystal lattice, which is determined by the potential energy between the neighboring molecules. The thermal motion of the H20 molecules is restricted but is not completely inhibited. The H20 molecules vibrate with a small amplitude at a given position. As the temperature of the ice in creases, the vibration of the H20 molecules in the ice becomes strong. Finally, each of the H20 molecules begins to part from the position deter mined by the potential energy, and the transition from ice (solid state) to water (liquid state) occurs (at 0°C). This is the melting of ice, and the en ergy for the transition is the heat of melting. In this stage, the thermal mo tion of the H20 molecules in water is not restricted as strongly as that in ice but is not completely free because the kinetic energy of the H20 molecules is not yet larger than the potential energy. Therefore, the H20 molecule vibrates around the lattice with neighboring H20 molecules.
