Chem 125 - 7 - Chapter 9

Chem 125 - 7 - Chapter 9 - Chapter 9 Thermochemistry!...

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Chapter 9 – Thermochemistry! Thermodynamics – the science of the relationships between heat and other forms of energy. Thermochemistry – the study of the quantity of heat absorbed or evolved by chemical reactions.
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Energy and Heat Heat – The kinetic energy that flows from a hot body to a cold body. Energy total kinetic potential E E + E + Internal Energy (U) =
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Kinetic and Potential Energy Kinetic energy – The energy an object has when it is moving. What kinds of motion are there? Potential energy – The stored energy an object has because it is either attracted or repelled by some other object. There is no single equation that can be used to calculate an object’s potential energy. 2 kinetic E = 1 2mv
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Internal Energy (U) The sum of the kinetic and potential energies of the particles making up a substance. – Distinguish between E K , E P and U for these
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The First Law of Thermodynamics The change in internal energy of a system, U, results from an exchange of energy, in the form of heat and/or work, between a system and its surroundings. w q ΔU + =
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Heat (q) Heat (q) is the energy transferred as a result of differences in temperature between a system and surroundings. q > 0: Heat is positive if heat is absorbed by a system from its surroundings (the system gains energy). q < 0: Heat is negative if heat is given off by a system to its surroundings (the system loses energy).
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Work (w) Work is a method of exchanging energy between the system and surroundings. Work is defined as the energy required to move an object a distance z against an opposing force of magnitude F. z F w - =
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Sign Convention for W When the surroundings do work on the system, the system gains energy. Therefore, w > 0. When the system does work on the surroundings, the system loses energy. Therefore, w < 0.
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Expansion (PV) Work M dz g F = mg M f i V ext ext V w P dV = P V = - ext
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The Units of Energy SI unit: 1 Joule (J) = 1 kg∙m 2 /s 2 Non SI unit: 1 calorie (cal) = 4.184 J One calorie is the amount of energy required to raise the temperature of one gram of water by one degree Celsuis. One dietary calorie is equal to one kilocalorie.
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System and Surroundings System – The substance or mixture of substances under study in which a change occurs is called the system. Surroundings
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This note was uploaded on 04/09/2008 for the course CHEM 125 taught by Professor Bussell during the Fall '06 term at Western Washington.

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Chem 125 - 7 - Chapter 9 - Chapter 9 Thermochemistry!...

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