Keq for GASES Kp

Equilibrium and Pressure 2SO2(g) + O2(g) 2SO3(g) If reactants and products are gases, partial pressures of each species can be used to determine the equilibrium The total pressure = PSO2 + PO2+ PSO3

Concentration of Gases For reactions that contain gases: PV = nRT P = (n/V)RT P = CRT “C” is concentration in mol/L C = P/RT The concentration of a gas is directly proportional to the pressure exerted by the gas.

Problems Involving Pressure 2 NO2 (g) N2O4 (g) KP = 7.63atm at 300K. What are the equilibrium pressures of NO2 and N2O4 if a flask initially contains 1.000 atm of NO2? What is the value of the Kc at 300K.

Relating Kp and Kc Kp = Kc (RT)Δn Kp = partial pressure constant using atm Kc = molar concentration constant using M R = ideal gas constant, 0.0821 L-atm/mol-K T = absolute temperature in K Δn= moles of product – moles of reactants

DIFFERENT TYPE OF K

Ksp - Solubility Product of a Salt KCl (s) K+ (aq) + Cl- (aq) CaCl2 (s) Ca+2 (aq) + 2 Cl- (aq)

Ksp values Acid Formula Ka value Potassium nitrate KNO3 Very large Calcium sulfate CaSO4 3.0 x 10 -5 Lead (II) chloride PbCl2 1.7 x 10 -5 Lead (II) iodide PbI2 1.0 x 10 -8 Silver iodide AgI 1.0 x 10 -16 Silver sulfide Ag2S 1.0 x 10 -49 Is any substance truly insoluble? Why are some substances more soluble than others?

Problem Involving Ksp The Ksp of lead (II) chloride at 298K is 1.7 x 10-5. Write the dissociation of lead (II) chloride in water. Write the expression for the solubility product, Ksp, of lead (II) chloride. Determine the concentration of the chloride ions and the lead ions of a saturated solution at 298K.

Kw - Autoionization of Water Kw is 1.00 x 10-14 at room temperature. What would be the Keq expression? How does the [H3O+] compare to the [OH-]? What would be the [H3O+]? What would be the pH? Like any other equilibrium constant, the value of Kw varies with temperature.

Ka – Acid Dissociation Constant Arrhenius acids dissociate to produce hydrogen ions in solution. What is the difference between a strong and weak acid?

Ka values Acid Formula Ka value Perchloric acid HClO4 Very large Hydrochloric acid HCl Nitric acid HNO3 Sulfuric acid H2SO4 Phosphoric acid H3PO4 7.5 x 10 -3 Citric acid H3C6H5O7 7.1 x 10 -4 Hydrofluoric acid HF 3.5 x 10 -4

Problem Involving Ka Acetic acid, HC2H3O2, has a Ka of 1.7 x 10-5 at 298K. Write the expression for the acid dissociation of acetic acid. Determine the concentration of the hydrogen ions and the acetate ions at 298K of a 1.0 M acetic acid.

Kb – Base Dissociation Constant Arrhenius bases dissociate to produce hydroxide ions in solution. Some bases dissociate completely; other dissociate only partially. This determines if a base is strong or weak. 14

Kb values Based Formula Ka value Potassium hydroxide KOH Very large Sodium hydroxide NaOH Zinc hydroxide Zn(OH)2 9.6 x 10 -4 Methylamine CH3NH2 3.7 x 10 -4 Ammonia NH3 1.8 x 10 -5

Problem Involving Kb 1.0 moles of pure ammonia gas is dissolved to make a 1 Liter solution at 298K. Ammonia partially dissociates to produce the ions shown below. Ammonia, NH3, has a Kb of 1.8 x 10-5 at 298K. Write the expression for the Kb of ammonia. What is the hydroxide concentration at equilibrium? What is the pH of a 1.0 M NH3(aq) solution? 16

DIFFERENT TYPE OF K MULTISTEP REACTIONS 17

Overall Keq A + B  C Keq = K1 C  D + E Keq = K2 A + B  D + E Keq = K1K2 18

Practice Problem Mg(OH)2 (s) Mg+2(aq) + 2 OH- (aq) Ksp = 5.6 x 10-11 MgF2 (s) Mg+2(aq) + 2 F- (aq) Ksp = 5.8 x 10-10 NET REACTION: 2 F- (aq) + Mg(OH)2 (s) 2 OH- (aq) + MgF2 (s) Manipulate the equations for the dissolving of Mg(OH)2 and MgF2 to obtain the net ionic reaction. Calculate the Keq of the net ionic reaction. 19