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16-2: The Law of Chemical Equilibrium
Remember…
• Chemical equilibrium is achieved when the rate of the forward rxn is equal to the rate of the reverse reaction
The Equilibrium Constant
• aA + bB cC + dD• Keq = [C]c[D]d
• [A]a[B]b
Example
• 6CO2 + 6H2O C6H12O6 + 6O2
Chemical Equilibrium
• Every rxn has specific Keq at a given temperature.
• Remember that we are considering the conc. at equilibrium of each substance raised to the power of its coefficient. Conc. are in molarity
Law of Chemical Equilibrium
• Law of Chemical Equilibrium: every reversible rxn proceeds to an equilibrium state that has a specific ratio of the conc of reactants to products expressed by Keq
• If Keq is very large (much greater than one), then the rxn lies to the right
• If Keq is very small (much less than one), then the reaction lies to the left.
Law of Chemical Equilibrium
• Homogeneous equilibrium: all reactants and products are in the same state
• Heterogeneous equilibrium: reactants and products are in more than one state
Law of Chemical Equilibrium
• In the Keq expression, solids and liquids do NOT actually appear. Why? Their concentrations do not substantially change and are figured into the equilibrium constant
• Reaction quotient (Q): used to determine if a reaction is at equilibrium
• If K>Q, then the reaction will proceed to the right
• If K<Q, then the reaction will proceed to the left
• If K=Q, then the reaction is at equilibrium