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Equilibrium

Equilibrium. By: Blaise McNeese and Lauren James. What is Equilibrium?. Consider the reaction aA+bB <----> cC+ dD  Reactants A and B are forming products C and D. Now consider the reverse reaction of reactants C and D producing products A and B.

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Equilibrium

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  1. Equilibrium By: Blaise McNeese and Lauren James

  2. What is Equilibrium? • Consider the reaction aA+bB <----> cC+ dD •  Reactants A and B are forming products C and D. • Now consider the reverse reaction of reactants C and D producing products A and B. • Both these reactions occur until their rates are equal. And since the reaction never truly ends the rates of A, B, C, and D are constant. •  this is equilibrium-two exactly opposite reactions are occuring at the same place, time, and with the same rates of reaction. • When the system reaches equilibrium, the reaction doesn't end. • Dynamic Equilibrium-when a reaction is proceeding at the same rate and the chemical species are constant. Ie. The reaction is forever continuous.

  3. Equilibrium as Q • However, at equilibrium the concentrations of the products and reactants are constant, NOT EQUAL. • A relationship between the products and reactants is defined as Q. For the reaction on the last slide, Q is         [A]a[B]b       [C]c[D]d • When writing Q, products are always over the reactants.

  4. Ka, Kw, Kb, and Kp • Kc= equilbrium constant • Ka= weak acid • Kb= weak base • Kw= constant of water= 1.0x10-14= KaxKb @25oC •  Kp= gas pressure • Large Kc means it lies to the right, small Kc means it lies to the left.

  5. LaChatlier's Priciple • If you mess with a reaction at EQ, it will shift to become equalized again. •  Pressure and volume only effect the system if a gas is involved. • Temperature- you need to know if the reaction is endothermic or exothermic.            - If it is endothermic- heat is a reactant            - If it is exothermic- heat is a product • If we take the reaction: N2(g) + 3H2(g) <---> 2NH3(g) + heat • then a high temperature would cause the reaction to shift left, resulting in more H and N. A lower temp leads to more NH3

  6. Changes in Pressure and Volume • N2 (g)+3H2 (g) <---> 2NH3 (g) • Raising the volume causes a shift left - why? • Lowering the volume causes a shift right - why?

  7. How to Change Pressure • Change the Volume or the Concentration • To raise Pressure                     Volume                     Concentration •   To lower Pressure                      Volume                      Concentration

  8. A bit of Titrations      • When titration a strong acid and strong base EQ is at a pH of 7. • Strong A and Weak B-acidic (pH<7) • Weak A and Strong B- basic (pH>7) • Weak A and Weak B- (compare K values. Larger K determines the solution's pH)

  9. A bit of Solutions    • Used with slihgtly soluable salts. • ie. PbS04(s) <---> Pb+2(aq) + S04-2(aq) • The solution is saturated when no more PbS04 will dissolve. • If we add, say, NaS04 to the solution then it will shift to the right. Why? • Ksp= [Pb+2][S04-2]      

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