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Le Chatelier’s principle and more... 7.2.3-7.2.5

Le Chatelier’s principle and more... 7.2.3-7.2.5. Le Chatellier’s principle and more. Nice video- 20 minutes Another good one- 15 minutes

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Le Chatelier’s principle and more... 7.2.3-7.2.5

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  1. Le Chatelier’s principle and more...7.2.3-7.2.5

  2. Le Chatellier’s principle and more... • Nice video- 20 minutes • Another good one- 15 minutes • states when a system in chemical equilibrium is disturbed by a change, the system shifts in a way that tends to counteract this change of variable • a change imposed on an equilibrium system is called a stress • a stress usually involves a change in the temperature, pressure, or concentration • the equilibrium always responds in such a way so as to counteract the stress

  3. McGraw Hill Flash animation Stress 1. Temperature change Haber Process again DH = + 92 kJ N2(g) + 3H2(g) 2NH3(g) DH = - 92 kJ • this is the ONLY stress that would actually change Kc • increasing temperature • favors the “cold side”/endothermic/the reaction that needs heat • adding heat is like adding more products tothe reaction so therefore it shifts left to counteract stress • Kc decreases • decreasing temperature • favors the “hot side”/exothermic/the reaction that gives off heat • Kc increases

  4. McGraw Hill Flash animation Stress 2. Pressure change Haber Process again N2(g) + 3H2(g)  2NH3(g) DH = - 92 kJ • an increase in pressure causes the equilibrium to shift in the direction that has the fewer number of moles • results in a decrease in N2 and H2 and an increase in NH3 • an decrease in pressure causes the equilibrium to shift in the direction that has the most number of moles • results in a an increase in N2 and H2 and an decrease in NH3 • does NOT affect the equilibrium constant Kc

  5. McGraw Hill Flash animation Stress 3. Concentration change Haber Process again N2(g) + 3H2(g)  2NH3(g) DH = - 92 kJ • the equilibrium responds in such a way so as to diminish the increase or equalize the ratio • increasing concentration of reactants shifts the reaction to the right (forward, more product) • increasing concentration of products shifts the reaction to the left (reverse, more reactants) • does NOT affect the equilibrium constant Kc

  6. Practice Problem • Predict the effect of the following changes on the reaction in which SO3 decomposes to form SO2 and O2. 2 SO3(g)  2 SO2 (g) + O2 (g) Ho = 197.78 kJ • increasing the temperature of the reaction • shifts right • increasing the pressure on the reaction • shifts left • adding more O2 when the reaction is at equilibrium • shifts left • removing O2 from the system when the reaction is at equilibrium • shifts right

  7. Catalyst • the same process still has to happen, catalysts just help out by lowering the activation energy • increase the RATE of a reaction….and therefore the decrease the time in which equilibrium is reached • they speed up the forward and reverse reactions equally • therefore decreases the time required for the system to achieve equilibrium • less time equals $$$ when making chemicals

  8. Le Chatelier’s Principle – Summary 8

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