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Phase Change Energy

[Article 16 by fmyhr, 1998-07-19 | Review this article]

Phase Change Energy: A form of chemical energy that is associated with physical phase changes, such as ice changing to liquid water. In a phase change there are no chemical bonds broken or formed, but the physical arrangement of the water molecules changes. Each water molecule has parts with positive electric charge (near the hydrogen atoms) and negative electric charge (near the oxygen atom). Because like charges repel and opposite charges attract, when two water molecules get close to one another they try to align themselves so that the positive area on one is close to the negative area on the other. In ice the water molecules arrange themselves into crystals in which each molecule has a fixed set of neigbor molecules, and its positive parts line up as well as possible with negative parts of its neighbors. When ice melts to liquid water, the individual water molecules become dislodged from this crystal and flow over one another, no longer keeping fixed neighbors. They're no longer able to stay aligned with their neighbors as they did in the ice. This phase change from solid ice to liquid water requires energy. This phase change energy is one reason why it's better to cool down your favorite beverage by adding an ice cube rather than adding an equal amount of very cold water. The fridge in your kitchen uses phase change energy (from liquid to gas this time) to cool your food.

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