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# 09 - 2 Change in pressure N 2 O 4 2NO P = nRT/V Pressure...

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10/29/09 Chapter 6 Consider 3 changes to conditions that impact equilibrium: 1)Changes in concentration (Partial pressure for gases of a constituent) 2)Change in total pressure 3) Change in Temperature Le Chatelier’s Principle: when a stress is applied to a system in equilibrium, the equilibrium shifts in a direction to relieve that stress, restoring the system to its original state H 2 + I 2  2HI 1)Change in concentration of 1 reactant Once the system is at equilibrium, what happens if more I 2 is added This is exactly what Le Chatelier’s principle predicts: if we add I 2 , the reaction will shift to the right to relieve that stress From kinetic of molecular viewpoint when more I 2 is added, we increase the probability of collism with H 2 HI will form at a greater rate An increase in the concentration of 1 of the reactants in an equilibrium causes a shift in the equilibrium to decrease the concentration of the added material

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Unformatted text preview: 2) Change in pressure N 2 O 4 2NO P = nRT/V; Pressure can be reduced by shifting the equilibrium to the left What happens if the volume is decreased by ½? WE see that in response to an increase in total pressure, the equilibrium shifts to the left 3) Change in Temeprature Need to know some thermochemical data to make a prediction H 2 + I 2 2HI ∆H= -10.46 kJ/mol If the temperature increases, less HI is formed, and the euqiloibrum shifts to the left If the temperature decreases, more HI is formed, and the equilibrium shifts to the right In accord with Le Chatelier’s principle: the reaction shifts in a direction to counter the effect of added heat Temperature & Le Chatlier’s Principle Quantitative Insight: requires a relationship between K and ∆H 10/29/09 Cl 2 2Cl ∆H=243.5 kJ/mol at 600 K K p- 4.8 x 10-16...
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