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Lect+13+08 - This lecture's goal is a plain language...

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This lecture’s goal is a plain language understanding of Energy and First Law Concepts Calorimeter operation Forms of energy Thermal energy in Molecules First Law Quantities Internal Energy and Enthalpy Review of a few relevant calculus concepts scattered through the lecture
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“Bomb” Calorimetry Used to measure heats and heat capacities Calibrate total heat capacity of the “can” by observing increase in temperature from know electrical energy input (electrically generated heat) Observe change in temperature with unknown heat input for phase change, or temperature change with chemical reaction (eg. combustion)
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Forms of Energy On the level of discrete (classical) particles, all energy can be classified as (1) kinetic or (2) potential . (1) Kinetic energy is the energy of motion, K = (1/2) mv 2 (2) Potential energy is associated with forces, F x = - U/ x (the force always tends to lower the potential energy) Two important forms of potential energy are: electrical : U el = q 1 q 2 /(4 πε 0 R); F el = -q 1 q 2 /(4 πε 0 R 2 ) gravitational : U g = Gm 1 m 2 /R; F g = -Gm 1 m 2 /R 2
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Interchange of Kinetic and Potential Energy At the top of its trajectory, the ball stops and has no kinetic energy. At the top the ball has more potential energy because it has been higher in the gravitational field. At the bottom of the trajectory, the ball is moving rapidly and so its kinetic energy is highest. However, the ball loses potential energy as is rolls to a lower point in the gravitational field.
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