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Homogenous & Heterogeneous Equilibria

Homogenous & Heterogeneous Equilibria. Homogenous Equilibria  equilibrium conditions for rxns in which all the reactants & products are in the same state eg. 2CO (g) + O 2(g)  2CO 2(g) Heterogenous Equilibria

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Homogenous & Heterogeneous Equilibria

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  1. Homogenous & Heterogeneous Equilibria Homogenous Equilibria  equilibrium conditions for rxns in which all the reactants & products are in the same state eg. 2CO(g) + O2(g) 2CO2(g) Heterogenous Equilibria  equilibrium conditions for rxns that involve substances in more than 1 state eg. NH4Cl(s)  NH3(g) + HCl(g)

  2.  Earlier, we expressed [] as M (for gases) [] of solids & liquids in a chem. rxn. do not change substantially and so are not included in the equilibrium constant [solid & liquid]  change during a rxn, left out of Keq  eg. C(s) + H2O(g) CO(g) + H2(g) Keq = [CO][H2] . [H2O]

  3. The Reaction Quotient  It is hard to tell if a rxn. has reached equilibrium  The “reaction quotient” (Q) is used to determine if a rxn. is @ equilibrium  Q is calculated like Keq except the []’s are taken @ the time of measurement, not necessarily @ equilibrium  Thus we can compare the value of Q to the value of Keq to see how the rxn. is progressing  Rxn. is @ equilibrium when Keq = Q

  4. Example: At 473°C, nitrogen gas is reacted with hydrogen gas to produce ammonia. A measurement was taken as the reaction proceeded and it was found that there was 0.15 M of nitrogen gas, 0.0020 M of hydrogen gas, and 0.15 M of ammonia. Given that the Keq is 0.105, is the reaction at equilibrium?

  5. N2(g) + 3H2(g) 2NH3(g) temp. = 473°C [NH3] = 0.15 M Keq = 0.105 [N2] = 0.15 M [H2] = 0.0020 M Keq = [NH3]2Q = (0.15)2 . [N2][H2]3 (0.15)(0.0020)3 = 1.9 x 107 Keq Q this rxn. is NOT @ equilibrium

  6. Which direction will rxns proceed to reach equilibrium? Q < Keq Q is less thanKeq  denominator is too large and numerator is too small  too much of reactants, too little of products  rxn. will proceed to the right (in the direction of products)

  7. Q > Keq Q is greater thanKeq  denominator is too small and numerator is too large  too much products, too little reactants  rxn. will proceed to the left (in the direction of reactants)

  8. Example: COCl2(g) CO(g) + Cl2(g)Keq = 170 At the time of measurement: [CO] = 0.15 M [Cl2] = 0.15 M [COCl2] = 1.1 x 103 M Is the rxn. @ equilibrium? If not, which direction will it proceed?

  9. Q = [CO][Cl2] = (0.15)(0.15). = 20. [COCl2] (1.1 x 103) Q < Keq thus rxn. is NOT @ equilibrium  there is too much reactants  rxn. will shift right in the direction of products

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