L24-Chemical_Dynamics-Corrected

L24-Chemical_Dynamics-Corrected - Bond Energies Part IV:...

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Part IV: Chemical Dynamics Thermodynamics and Thermochemistry Enthalpy, Spontaneity and Entropy 1 Bond Energies 2 ! H rxn 0 = B . E . reac " # B . E . prod " N 2 ( g ) + 3 H 2 ( g ) ! 2 NH 3 ( g ) ! H rxn 0 = ! H NN + 3 ! H HH [ ] " 6 ! H NH [ ] Bond Energy Bond energies can be used to calculate ! H for a reaction in the gas phase 3 So where are we now? 1 st Law of Thermodynamics total energy of the universe is conserved Energy: the capacity to do work or transfer heat Heat transfer measured as enthalpy (H) ! H is what we measure H can’t be measured directly - ! H: exothermic reaction + ! H: endothermic reaction 4
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So where are we now? What good is studying thermodynamics? 1. Provides information about a reaction ! spontaneity of a reaction under a given set of conditions What do we mean by “spontaneous”? 5 Spontaneous or Not? Spontaneous? Ice Melting at Room Temperature Yes! Ice Freezing at R.T. No Ice Melting at -2°C No Table sugar being converted to CO 2 and H 2 O Yes! Iron rusting out in the open
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This note was uploaded on 09/24/2009 for the course CHEM 333 taught by Professor Baird during the Spring '09 term at UC Davis.

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L24-Chemical_Dynamics-Corrected - Bond Energies Part IV:...

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