Calorimetry Worksheet - C alorimetry Worksheets Phase...

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Calorimetry Worksheets Phase Changes Imagine a simplified model of a solid as tiny particles bonded together by springs. The spring represent the electromagnetic forces between the particles. If the thermal energy of a solid is increased, both the potential and kinetic energy of the particles increase. The temperature is a measure of the average kinetic energy of the particles. At higher temperatures, the forces between the particles are no longer strong enough to hold them in fixed locations. Eventually, the particles become free to slide past each other. The substance has changed from a solid to a liquid. The temperature at which this occurs is called the melting point. When a substance is in the process of melting, added thermal energy increases the potential energy of particles, breaking the bonds holding them together. The added thermal energy does not increase the kinetic energy of the particles. Thus, the temperature does not increase. The amount of energy needed to melt a unit mass of a substance is called the heat of fusion of that substance. For example, the heat of fusion of ice is 3336 J/g. If one gram of ice at its melting point, 0 o C, absorbs 3336 J, it will become 1 gram of water at the same temperature, 0 o C. The added energy causes a change in state but not in temperature. After the substance is totally melted, a further increase in thermal energy once again increases the temperature. Added thermal energy increases both the kinetic and potential energy. As the temperature increases, some particles in the middle of the liquid obtain enough energy to break free from other particles. A tiny bubble of vapor is formed and rises to the surface. The liquid begins to boil. Any added thermal energy is
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