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The Equilibrium Constant Expression

The Equilibrium Constant Expression. Here comes K !!. D G = D H – T D S. Describing equilibria. The state of equilibrium can be described in two ways; percentage reaction equilibrium constant, K eq The progress or status of the equilibrium can be assessed through the;

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The Equilibrium Constant Expression

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  1. The Equilibrium Constant Expression Here comes K!!

  2. DG = DH – TDS

  3. Describing equilibria • The state of equilibrium can be described in two ways; • percentage reaction • equilibrium constant, Keq • The progress or status of the equilibrium can be assessed through the; • reaction quotient, Q.

  4. Percent reaction at equilibrium • PercentageReaction • The product measured at equilibrium expressed as a percentage of the theoretical yield.

  5. Percent reaction at equilibrium • Percentage reaction can be used to classify chemical reactions at equilibrium.

  6. Equilibrium Constant • At equilibrium the concentration of the reactants and products are constant and the equilibrium constant, Kcor K or Keq, is a mathematical expression of these concentrations. • Discovered in 1864 by two Norwegian chemists, Cato Maximilian Guldberg & Peter Waage it is also called the Equilibrium Law • if a chemical system is in equilibrium, there will be a constant ratio between the concentrations of the products and the concentrations of the reactants

  7. Equilibrium Constant (Keq or Kc or K) For the generalchemical reaction: aA + bBDcC + dD

  8. Equilibrium Constant (Keq or Kc or K) Where; aA + bBDcC + dD A, B, C, and D are the concentrations of the reactants and products in gas or aqueous phases, after the reaction has reached equilibriumand the concentrations are no longer changing, and a, b, c, and d are the coefficients in the balanced chemical equation.

  9. Equilibrium Constant characteristics • The product of the molar concentrations of the products is always in the numerator, while the product of the molar concentration of the reactants in in the denominator. • The exponents are the same as the coefficients in the balanced reaction. • The constant is dimensionless. • Liquids and solidsnever appear in the expression as their concentrations are constant. • The equilibrium constant value is specific to the temperature of the system.

  10. The meaning of Equilibrium Constant values • Keq > 1 The products are favoured and the equilibrium lies far to the right. If the Keq value is greater than 1010, it is considered to go to completion (a quantitative reaction) • Keq = 1 The concentrations of the reactants and products are approximately equal. • Keq < 1 The reactants are favoured and the equilibrium lies far to the left. If the Keq value is greater than 10-10, it is considered to be a non-reacting reaction.

  11. Keq & Percent reaction comparison Reactants [ ] Products Time Reactants Products Products [ ] [ ] [ ] Reactants Reactants Products Time Time Time

  12. Uses for the Equilibrium Constant • Testing to see if an equilibrium has been established. • Predicting the effects of changing the concentrations, temperature and pressure conditions of the system. • Calculating the equilibrium concentrations.

  13. Analyzing the Equilibrium Law ICE TABLE • In the quantitative analysis of an equilibrium system is may be advantageous to chronicle the progression of the system over time. • The ICE table is a method of recording the Initial concentration, the Change in concentration during the equilibrium process, and the final Equilibrium concentrations.

  14. ICE Table 2 CO2(g)D2 CO(g) + O2(g) Initial concentrations of reactants & products [CO2(g)] Reduction in [CO2(g)] by “2x” Changes occur in the concentrations as the reactants become used up (decrease) & the products are created (increased) in proportions predicted in the balanced chemical reaction. [CO2(g)] Concentration (mol/L) Increase in [CO(g)] by “2x” [CO(g)] [O2(g)] Once the equilibrium process has stabilized, Equilibrium concentrations will be established Increase in [O2(g)] by “x” [O2(g)] [CO(g)] Time (s)

  15. ICE Table In the following chemical system, a 0.250 mol/L sample of carbon dioxide (CO2(g)) forms an equilibrium as suggested in the following chemical equation. 2 CO2(g)D2 CO(g) + O2(g) 2 CO2(g)D 2 CO(g) + O2(g) Change concentrations Equilibrium concentrations Initial concentrations Time (s)

  16. ICE Table • Initial, Change in & Equilibrium concentrations are accounted for in the ICE table. • The ICE Table is an effective tool in the analysis & processing of quantitative characteristics in an equilibrium system.

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