Dr. S. M. Condren Chapter 14 Chemical Equilibrium

Dr. S. M. Condren Chemical Equilibrium The state of a chemical reaction in which its forward and reverse reactions occur at equal rates so that the concentration of the reactants and products does not change with time.

Dr. S. M. Condren Law of Mass Action aA + bB + cC +... pP + qQ + rR +... Equilibrium Constant [P] p [Q] q [R] r... K = [A] a [B] b [C] c...

Dr. S. M. Condren Catalytic Methanation Reaction

Dr. S. M. Condren Meaning of Equilibrium Constant K>>1: reaction is product-favored; equilibrium concentrations of products are greater than equilibrium concentrations of reactants. K<<1: reaction is reactant-favored; equilibrium concentrations of reactants are greater than equilibrium concentrations of products.

Dr. S. M. Condren If K = 100 = [I 2 in CCl 4 ] / [I 2 in water] for the equilibrium I 2 in water = I 2 in CCl 4 What is K for the reverse reaction, I 2 in CCl 4 = I 2 in H 2 O? 100, 1, 0.01

Dr. S. M. Condren Autoionization of Water H 2 O + H 2 O H 3 O + + OH - [H 3 O + ][OH - ] K = [H 2 O] 2 K w = K [H 2 O] 2 = [H 3 O + ][OH - ] = 1.0 x

Dr. S. M. Condren Analogy in Semiconductors | | | | -Si:Si- -Si + :Si- + e - | | | | | | -Si:Si- h + + e - | | K = h + * e -

Dr. S. M. Condren e - and h + in Semiconductors Production Recombination electrons (e ) – holes (h ) + Electron energy conduction band valence band Si e – + h E g conduction band valence band

Dr. S. M. Condren Autoionization Equilibria

Dr. S. M. Condren e - and h + in Semiconductors + h Si e – + h e – (–)(+)

Dr. S. M. Condren Doping

Dr. S. M. Condren Donors and Acceptors in Silicon conduction band } valence band donors M  M + e + – }

Dr. S. M. Condren Which dopant will act as an acceptor for Si? B, Ge, As As a donor? B, Ge, As

Dr. S. M. Condren Fermi Level

Dr. S. M. Condren Le Chatelier's Principle If a stress, such as a change in concentration, pressure, temperature, etc., is applied to a system at equilibrium, the equilibrium will shift in such a way as to lessen the effect of the stress.

Dr. S. M. Condren Gas Phase Equilibrium catalysis N 2(g) + 3 H 2(g) 2 NH 3(g) + heat high pressure and temperature

Dr. S. M. Condren The Principle of Le Chatelier Changes in Concentration or Partial Pressure for N 2(g) + 3 H 2(g)  2 NH 3(g) an increase in N 2 and/or H 2 concentration or pressure, will cause the equilibrium to shift towards the production of NH 3

Dr. S. M. Condren The Principle of Le Chatelier Changes in Concentration or Partial Pressure for N 2(g) + 3 H 2(g)  2 NH 3(g) likewise, a decrease in NH 3 concentration or pressure will cause more NH 3 to be produced

Dr. S. M. Condren The Principle of Le Chatelier Changes in Temperature for N 2(g) + 3 H 2(g)  2 NH 3(g) + heat for an exothermic reaction, an increase in temperature will cause the reaction to shift back towards reactants

Dr. S. M. Condren The cobalt complexes participating in the equilibrium below comprise a humidity sensor. From Le Châtelier's principle, when the sensor is moist (excess H 2 O), what color is the cobalt complex? pink, blue

Dr. S. M. Condren A competition experiment involves O 2 and CO vying for hemoglobin (Hb) sites, defined by the equilibrium Hb(O 2 ) CO = Hb(CO) 4 + 4O 2 From Le Châtelier's principle, how is CO poisoning reversed? decrease O 2 pressure, increase O 2 pressure, remove Hb

Dr. S. M. Condren Heterogeneous Equilibrium CaCO 3(s) + heat CaO (s) + CO 2(g)