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Equilibrium Expression

Chemist’s generally express the position of equilibrium in terms of numerical values These values relate the amounts of reactants to products at equilibrium Consider this hypothetical rxn…. wA + xB. yC + zD. Equilibrium Expression.

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Equilibrium Expression

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  1. Chemist’s generally express the position of equilibrium in terms of numerical values These values relate the amounts of reactants to products at equilibrium Consider this hypothetical rxn… wA + xB yC + zD Equilibrium Expression • Where “w” mols of reactant A and “x” mols of reactant B react to give “y” mols of product C and “z” mols of productD at equil.

  2. We can write a mathematical expression to show the ratio of product concs to reactant concs called anequilibrium expression [C]y [D]z [A]w [B]x Equilibrium Expression • The concentration of each substance is raised to a power equal to the # of mols of that substance in the balanced rxn eqn. • The square brackets indicate concentration in Molarity (mol/L)

  3. The resulting ratio of the equilibrium is called theequilibrium constant or Keq The Keq is dependent on the temp If the temp changes so does the Keq Keq= [C]y [D]z [A]w [B]x Equilibrium Expression NOTE: pure solids and liquids cannot change concentration, therefore they are not included in the equilibrium expression

  4. Equilibrium constants provide valuable chemical information They show whether products or reactantsare favored in a rxn always written as a ratio of products over reactants a value of Keq > 1 means that products are favored Keq < 1 than reactants are favored Equilibrium Constant

  5. Keq > 1 products favored at equil Keq < 1 reactants favored at equil

  6. Sample Problem 1 Dinitrogen tetroxide (N2O4), a colorless gas, and nitrogen dioxide (NO2), a brown gas, exist in equilibrium with each other according to the following eqn: N2O4(g) 2NO2(g) A liter of gas mixture at 10C at equilibrium contains 0.0045mol N2O4 & 0.030 mol NO2. Write the Keq expression and calculate Keq for the reaction.

  7. Known: [N2O4] =.0045mol/L [NO2] =.030mol/L Unknown: Keq expression = ? Keq = ? Analyze: list what we know • At equilibrium, there is no net change in the amount of N2O4 or NO2 at any given instant

  8. The only product of the rxn is NO2, which has a coefficient of 2 in the balanced eqn The only reactant N2O4 has a coefficient of 1 in the balanced eqn The equilibrium expression is: [N2O4]1 [.030M]2 Keq= [.0045M]1 Calculate: solve for unknowns [NO2]2 Keq= • Keq is equal to: Keq= 0.20 • Keq < 1, therefore rxn doesn’t favor products

  9. A mixture at equilibrium at 827°C contains 0.552 M CO2, 0.552 M H2, 0.448 M CO, and 0.448 M H2O. CO2(g)+ H2(g)<==> CO(g) + H2O(g) Write the equilibrium expression for the above rxn. Calculate Keq at this temp? More CO2 is added to the system, which direction will the reaction shift? Are the reactants or products favored in this reaction? Classwork:

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