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TwoPoint0K

# TwoPoint0K - The TWO-POINT Method of Evaluating 0K Goal You...

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The TWO-POINT Method of Evaluating 0K Goal: You will use the direct relationship of Temperature with Volume to determine the Absolute zero. Background: The Ideal Gas Law, PV= nRT, contains four variables and the Ideal Gas Constant. The existence of four variables indicates that gas experiments can get very complicated very quickly if an experimenter doesn’t properly control his or her conditions. Typically, one controls two of the variables, then makes changes to a third, while measuring the fourth. It is common for a student to “do the math” with this Law, without thinking, and to arrive at an erroneous answer through an algebraic error. If one keeps one’s everyday experience (common sense) in mind, one can often catch these mistakes. To develop the common sense, the experimenter should review the qualitative interactions of these variable-pairs in those everyday cases that most resemble their carefully- defined conditions which hold 2 variables constant. For example, a metal gas cylinder (or aerosol can) is a typical example in which volume can be held constant and a balloon is a case where volume is allowed to vary. Specifically, one should test one’s common sense and consider: 1. A metal gas cylinder at room temperature (V and T constant). Adding more moles, n, and the pressure rises (a direct relationship). 2. A metal gas cylinder that is sealed (V and n constant). Heating it (T increases) and the pressure rises (a direct relationship) 3. A steel pressure tank on a steam engine, with a pressure-release valve (P and V constant). If T increases, some moles must escape out the pressure release valve (an inverse relationship). 4. A weather balloon at ground level (P and T constant). Adding more moles, n, the balloon gets bigger (a direct relationship). 5. A filled-balloon taken outside in winter (n and P constant). When the gas gets colder, the balloon shrinks (a direct relationship). 6. A weather balloon rising in the atmosphere (n and T constant). When the balloon rises, the balloon expands (an inverse relationship). The reasons for these changes are explained by the Kinetic theory of gases, which states that gas molecules are in constant motion, measured directly by T, and pressure is created by the collisions of the molecules with the inside walls of the sample container. Increasing the energy of those collisions (higher T) will cause increase in pressure in a fixed-volume container or

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TwoPoint0K - The TWO-POINT Method of Evaluating 0K Goal You...

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