Chapter 5 M - Spring, 2009 Spring, 2009 Thermochemistry...

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pring, 009 Spring, 2009 Thermochemistry
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` Thermochemistry - measurement & prediction of the effects of heat. Energy of reactants & products is important as is the gy p p transfer of energy. Key: Heat is a stoichiometric quantity. ` Heat (q)– involves transfer of energy between 2 objects with mperature differences temperature differences. Unit = calorie (cal) or joule; 1 cal = 4.184 J ` Temperature (T) – property that reflects the random motion p( ) pp y of particles in a particular substance. ` Thermal equilibrium – a condition in which temperature is constant throughout a material and no heat flow occurs from point to point.
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nergy ) apacity to do work or produce ` Energy (E) – capacity to do work or produce heat. Types: kinetic & potential. Energy unit = joule (J) ` Work is done when a force moves an object through a distance. ` 1 st Law of Thermodynamics : energy cannot be created or destroyed.
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` Potential: due to position or composition - can be converted to work PE = m x g x h (m = mass, g = force of gravity, and h = vertical distance) (chemical energy is a form of potential energy) inetic: ue to motion of the object ` Kinetic: due to motion of the object KE = 1 / 2 mv 2 (m = mass, v = velocity)
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` Depends only on the present state of the ystem - ot how it arrived there. system not how it arrived there. It is independent of pathway.
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` KE at the molecular level depends on the mass nd velocity of e particle Velocity epends and velocity of the particle. Velocity depends on temperature so KE depends on temperature also. s T KE As T , KE Total energy of matter at the micro level is sum of KE due to random motion and PE due to arrangement of g particles. ` One of the most important forms of PE at the atomic-molecular level arises from electrostatic interactions .
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` Coulombic attraction, not gravitational force, determines the potential energy of matter at the atomic level. Q 1 x Q 2 E el d E el is the electrostatic potential energy
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ystem: the part of the universe that is the ` System: the part of the universe that is the focus of a thermodynamic study. ` Surroundings: everything in the universe that is not part of the system. ` Universe = System + Surroundings ` An isolated system exchanges neither energy nor matter with the surroundings.
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eactions can evolve heat XOTHERMIC ` Reactions can evolve heat – EXOTHERMIC q < 0 heat from system Æ surroundings Ex. Liquid Æ solid (freezing) eactions can absorb heat NDOTHERMIC ` Reactions can absorb heat – ENDOTHERMIC q > 0 heat from surroundings Æ system x Ex. Solid Æ liquid (melting)
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he internal energy of a system is the ` The internal energy of a system is the sum of all the KE and PE of all of the components of the system.
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This note was uploaded on 02/22/2011 for the course CHEM 25 taught by Professor X during the Spring '06 term at Lehigh University .

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Chapter 5 M - Spring, 2009 Spring, 2009 Thermochemistry...

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