Lect+20+08

# Lect+20+08 - Lecture Goals You will have a plain language...

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Lecture Goals You will have a plain language understanding of the effect of stress on equilibrium conditions (LeChatelier) You will be able to use the reaction quotient to solve equilibrium problems. You will be able to use the enthalpy of reaction to determine the temperature dependence of equilibrium constants for reactions and phase changes. You will have a plain language understanding of the basis for Extraction and Separation Processes

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External Effects on Equilibrium A system in equilibrium subject to stress will react in a way that tends to counteract the stress - Le Chatelier You will be able to describe the effect of reactant / product pressure(concentration) changes You will be able to describe the effect of changes in reactor volume You will be able to describe the effect of changes in Temperature
• H 2 (g) + I 2 (g) 2HI(g) Initial conditions - no product initially With time equilibrium conditions are established Stress - Add hydrogen- no longer at equilibrium - with time equilibrium re- established Re-equilibration reduces hydrogen and increases HI(g) Time

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Sealed isothermal system with moveable piston • 2P 2 (g) P 4 (g) at equilibrium Expand - decrease pressure - increase dissociation Compress - increase pressure - decreased dissociation
Effect of Temperature on Equilibria 2NO 2 (g) N 2 O 4 (g) 2200 H = -58.02 kJ/mol - Reaction as written is exothermic Q = ( P N2O4 )/(P NO2 ) 2 K = 8.8 at 298 K Equilibrium constant (in atm) decreases with increasing temperature because exothermic equilibrium. At 25C more N 2 O 4 or NO 2 ? So with increasing temperature? ? More N 2 O 4 ? or Less N 2 O 4 ?

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2NO 2 (g) N 2 O 4 (g) 273 K in ice bath Mostly clear N 2 O 4 333 K in hot water bath Mostly brown NO 2
Direction of Change from the Reaction Quotient aA + bB cC + dD If Q>K then Q will decrease with time Less products

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