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