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Chemical Equilibrium

Chemical Equilibrium. What is Chemical Equilibrium?. Reversible Reaction - a chemical reaction in which the products can react to re-form the reactants. Chemical Equilibrium

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Chemical Equilibrium

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  1. Chemical Equilibrium

  2. What is Chemical Equilibrium? • Reversible Reaction -a chemical reaction in which the products can react to re-form the reactants. Chemical Equilibrium • the forward reaction equals the rate of its reverse reaction and the concentrations of its products and reactants remain unchanged How is it Written? • use double arrows 2HgO(s)  2Hg(l) + O2(g)

  3. The Equilibrium Expression • Equilibrium Constant -ratio of the concentrations of the products to the concentrations of the reactants • there is no unit and it is dependent on temperature Equilibrium Expression K= [C]x [D]y [A]n [B]m n,m,x,y are the coefficients and are raised to the power equal to the coefficient of the substance The [ ] represent the concentrations of the substances

  4. Equilibrium Constant Example • An equilibrium mixture of N2, O2, and NO gases at 1500 K is determined to consist of 6.4 x 10-3 M of N2, 1.7 x 10 –3 M of O2, and 1.1 x 10-5 M of NO. What is the equilibrium constant for the system at this temperature? • N2(g) + O2(g)  2 NO(g)

  5. Shifting Equilibrium • What is Le Chatelier’s Principle? • If a system at equilibrium is subjected to a stress, the equilibrium is shifted in the direction that tends to relieve the stress.

  6. What stresses or changes affect equilibrium? • Changes in Concentration a. Increase(add) a reactant or product will shift away from the added reactant or product b. Decrease ( remove) a reactant or product will shift toward the removed reactant or product

  7. Change in concentration cont. • A + B  C + D • Which way will it shift if we: • Add B • Shift right • Add C • Shift left • Remove A • Shift left • Remove D • Shift right

  8. Equilibrium stresses cont. • Changes in pressure • only affects equilibrium systems in which gases are involved a. If the pressure is increased,it will shift towards the side with the smaller number of molecules b. If the pressure is decreased, it will shift towards the side with the larger number of molecules.

  9. Change in pressure cont. N2(g) + 3H22NH3 What would happen if we increased the pressure? Shift right What would happen if we decreased the pressure? Shift left

  10. Equilibrium stresses cont. • Changes in Temperature a. Increase ( add) temperature will cause a shift away from the added temperature b. Decrease (removal) temperature will cause a shift toward the removed temperature

  11. Changes in temperature cont. 556 kJ + CaCO3(s)  CaO(s) + CO2(g) What would happen if we increased the temperature? Shift right What would happen if we decreased the temperature? Shift left

  12. States of matter in Equilibrium problems • Have you noticed that all the examples that I have used have only included the gas or aqueous state? Why? • The concentrations of pure substances in solids and liquids phases are not changed by adding or removing quantities of the substance • They are not included in the equilibrium expression.

  13. Solubility Product Constant • Is the product of the molar concentrations of its ions each raised to the power of its coefficients • Example: BaSO4(s)  Ba2+(aq) + SO42-(aq) Ksp= [Ba2+] [SO42-]

  14. Example of Ksp Consider the dissociation of the salt CaF2. CaF2(s)  Ca2+(aq) + 2F-(aq) At a temperature of 298 K, the concentration of Ca2+ ions is 2.2 x10-4 M, and Ksp for the salt is 1.46 x 10-10. What is the concentration of F- in the solution?

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