Ch6 - CHAPTER 6 THERMOCHEMISTRY Thermochemistry is the...

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CHAPTER 6 THERMOCHEMISTRY THERMOCHEMISTRY
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Thermochemistry Thermochemistry is the study of the changes in heat energy that accompany chemical reactions & physical changes.
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Thermochemical Definitions Thermochemical Definitions 3 types : Open – exchanges both matter & energy w/ surroundings ( e.g. an open pot of boiling water ) Closed – exchanges only energy w/ surroundings ( e.g. contents of a sealed container ) Isolated – exchanges nothing w/ surroundings (it has no contact w/ surroundings; e.g. an insulated thermos flask containing a hot liquid approximate such a system.) System : That small part of the Universe whose change we are going to measure .
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Thermochemical Definitions Thermochemical Definitions Both sys. & surr. are separated by a boundary , which can be real (e.g. glass walls of a beaker or walls of a balloon) or imaginary (e.g. imaginary line 300 nm above a metal’s surface that separates the air close to its surface from rest of atmosphere) Surroundings : Everything else that can exchange energy with the system . ( system + surroundings = universe )
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Energy exchange b/w a system & its surroundings
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Thermochemical Definitions Thermochemical Definitions Work ( w ) : The energy transferred when an object is moved by a force. Therefore: E = q + w (1 st law of TD) [ (delta) = (final value) - (initial value) ] Internal Energy ( E ) : The sum of the kinetic and potential energy of all the particles that make up a system. Heat ( q ) : Is the amount of energy transferred b/w a system and it’s surroundings as result of a temperature difference b/w them
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E = E final - E initial = E products - E reactants Energy diagrams for the transfer of internal energy (E) between a system and its surroundings.
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E = q + w
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The Sign Conventions for q , w and E q w + = E + + - - - - + + + - depends on sizes of q and w depends on sizes of q and w q = + : system gains heat; q = - : system loses heat. w = + : work done on system; w = - : work done by system.
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First Law of Thermodynamics First Law of Thermodynamics ( Law of Conservation of Energy ) “Energy can be converted from one form to another but cannot be created or destroyed” (i.e., the total energy of the Universe is constant) E Universe = E System + E Surroundings = 0
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E universe = E system + E surroundings Units of Energy Joule (J) Calorie (cal) British Thermal Unit 1 cal 4.184J 1 J = 1 kg*m 2 /s 2 1 Btu = 1055 J
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State Functions State Functions Properties of a system that depend only on the current state of the system, not on the path to get to the current states. * capital letters used: [e.g.s : E (internal energy), P (pressure), V (volume), T (temp), H H (enthalpy), S S (entropy), G G (free energy) ] * To find each quantity is to know the initial state and final state of the system, then: = (final state) - (initial state)
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ENTHALPY: ENTHALPY: Heat Content of a Reaction Heat Content of a Reaction
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Change in Enthalpy = H Change in Enthalpy = H Enthalpy is defined as a system’s internal energy
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This note was uploaded on 06/18/2008 for the course CHEM 103 taught by Professor Liebird during the Summer '08 term at Grand Rapids Community College.

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Ch6 - CHAPTER 6 THERMOCHEMISTRY Thermochemistry is the...

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