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Unformatted text preview: Thermochemistry Energy Thermochemistry is the study of energy. Energy is basically the ability of a system to supply heat or to perform work. E = Heat + Work You already know the 2 forms of energy: Kinetic Energy , the energy of motion. When atoms or molecules move, their mass and speed give them energy: If a molecule of hydrogen gas and a molecule of nitrogen gas have the same KE, then what can you say about their relative velocities? Potential Energy Potential energy is a little harder to understand (and to explain). It is internal, stored energy. It may be stored energy because of position, or it may be stored internally in chemical bonds. A ball or boulder on a hill has potential energy because of its position in space: if it gets pushed, it will roll down the hill, converting potential energy into kinetic energy (and other energies). A molecule has chemical bonds holding it together, and these require energy to break, so this is another type of internal stored potential energy. Units of Energy Scientists use the energy unit joule, J. The J is an abbreviated unit, as look at the complete units that you would get from the above equation. Sometimes we still use the old unit calorie, cal, where 1 cal = 4.184J (exact) If you look at your food label and it says 140 Cal, this is a food calorie, Cal, where 1 Cal = 1000 cal. The typical male is supposed to eat 2000 Cal/day. How many J is this? Conservation of Energy You learned the Law of Conservation of Mass (and Matter), and there is also a Law of Conservation of Energy, also called the First Law of Thermodynamics : Energy cant be created nor destroyed; it can only be converted from one form of energy to another. Energy cant be created nor destroyed; it can only be converted from one form of energy to another....
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