L13_equil3.115b_08

L13_equil3.115b_08 - L13: Le Chatelier Principle (1888): If...

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L13: Le Chatelier Principle (1888): If a stress is applied to a system at equilibrium, then the system readjusts, if possible, to reduce the stress. Change in rxn conditions: - reactant and/or product concenration/pressure - Temperature effect for exo-/endothermic rxns - Changing volume/pressure of system Le Chatelier's Principle http://www.chm.davidson.edu/java/LeChatelier/LeChatelier.html
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Changing reactant pressure: H 2 + I 2 2HI Increase of H 2 pressure takes the system out of equilibrium. System response: Reduce H 2 pressure; how? by converting H 2 to HI Why? To re-establish K
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Change of volume of system Use ideal gas law Compress: increase total concentration System response: go in direction that reduces number of particles Expand: decrease total concentration System response: reverse of above 3H 2 + N 2 2NH 3
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2NO 2 N 2 O 4 + Δ E equilibrium Elementary exothermic reaction Effect of temperature where Δ E E a -1 E a 1 = E a prd - E a rct Δ E > 0 : low T -> larger K, more products (exo) high T -> smaller K, more reactants Δ E < 0 (endo) : the reverse E Rxn coordinate E a 1 E a -1 Δ E 1 11 () 1 1 1 1 1 E a EE E aa RT RT RT E a RT kA e A A Ke e A Ae Δ −− == = =
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Effect of temperature (T) on K: Exothermic rxn: K decreases with increasing T Endothermic rxn: K increases with increasing T Δ E>0 Δ E<0 lnK = ln(A 1 /A -1 ) + ( Δ E/R)(1/T)
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Consider heat to be one of the reactants or products of a reaction Heat is given off
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L13_equil3.115b_08 - L13: Le Chatelier Principle (1888): If...

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