“Products over reactants, the coefficients are the powers” The Equilibrium Law “Products over reactants, the coefficients are the powers”

equilibrium constant OUTCOME QUESTION(S): C12-4-04 EQUILIBRIUM AND Keq Relate the concept of equilibrium to physical and chemical systems. Include: conditions necessary to achieve equilibrium. Write equilibrium law expressions from balanced chemical equations and solve problems involving equilibrium constants. Include: ICE tables Vocabulary & Concepts equilibrium constant 

aA + bB cC + dD Keq Equilibrium Law For a system at equilibrium (with constant temperature), a ratio of the concentrations of reactants over products raised to the coefficients of the equation equal a constant value. aA + bB cC + dD This new expression is connected to what we know about elementary reactions and rate kinetics… = Keq [A]a[B]b [C]c[D]d

Keq kf [A]a[B]b = kr [C]c[D]d For an elementary reaction, the forward and reverse reactions would have these rate laws: aA + bB cC + dD ratefwd = kf [A]a[B]b raterev = kr [C]c[D]d And at equilibrium rates are equal: kf kr = [A]a[B]b [C]c[D]d Keq kf [A]a[B]b = kr [C]c[D]d Rearranged we get… The ratio of rate constants was condensed to one constant, Keq, called the equilibrium constant.

“Products over reactants, the coefficients are the powers” When writing the equilibrium expression, omit solids (s) or liquids (l). Solids and Liquids don’t have concentrations, they have density – which is accounted for in the constant value C(s) + H2O(g) CO(g) + H2(g) The constant is generally abbreviated Keq Kc is using concentrations Kp is when using pressures = [CO][H2] [H2O] Kc {C}

“Products over reactants, the coefficients are the powers” Write the equilibrium expressions: N2 (g) + 3 H2 (g) 2 NH3 (g) = Kc [N2][H2]3 [NH3]2 2 Na(s) + Pb2+(aq) Pb(s) + 2 Na1+(aq) = Kc [Pb2+] [Na1+]2 Homogeneous equilibria Reactants and products are all in one state Heterogeneous equilibria Reactants and products in more than one state

If Kc = 1 [products] = [reactants] Keq value can indicate whether there are more products or reactants when equilibrium is reached: If Kc = 1 [products] = [reactants] aA + bB cC + dD Kinetic Region Equilibrium Region Kinetic Region Equilibrium Region Concentration Rate Reactants Reactants Products Products Time teqbm Time teqbm

If Kc > 1 [products] are favoured. Keq value can indicate whether there are more products or reactants when equilibrium is reached: If Kc > 1 [products] are favoured. aA + bB cC + dD Kinetic Region Equilibrium Region Kinetic Region Equilibrium Region Concentration Rate Reactants Reactants Products Products Time teqbm Time teqbm

If Kc < 1 [reactants] are favoured. Keq value can indicate whether there are more products or reactants when equilibrium is reached: If Kc < 1 [reactants] are favoured. aA + bB cC + dD Kinetic Region Equilibrium Region Kinetic Region Equilibrium Region Concentration Rate Reactants Reactants Products Products Time teqbm Time teqbm

equilibrium constant CAN YOU / HAVE YOU? C12-4-04 EQUILIBRIUM AND Keq Relate the concept of equilibrium to physical and chemical systems. Include: conditions necessary to achieve equilibrium. Write equilibrium law expressions from balanced chemical equations and solve problems involving equilibrium constants. Include: ICE tables Vocabulary & Concepts equilibrium constant