Equilibrium & Kinetics Dr. Ron Rusay Summer 2004 © Copyright 2004 R.J. Rusay

Dynamic Equilibrium “ The Pennies” Organize into groups of 3-4. Organize into groups of 3-4. Dr. R will assign your group a number. Dr. R will assign your group a number. In your group, select one person as: In your group, select one person as: 1) Money Keeper 2) Recorder 3) Transfer Agent (Calculating agent) 4) Auditor (Can be combined with #3) Send the Recorder to see Dr. R. for your accounting form. Send the Recorder to see Dr. R. for your accounting form. Be sure to record other group member names on the form. Be sure to record other group member names on the form. After recording all of the names send the Money Keeper to see Dr. R. for your capital stake. After recording all of the names send the Money Keeper to see Dr. R. for your capital stake. Await instructions for phase I. Await instructions for phase I.

Dynamic Equilibrium “ The Pennies” Phase I: Phase II: There will be 8 phases. You can begin and go through them at your own pace. Let Dr. R know when you have completed four phases. Stop at this point. Give Dr. R. the accounting form when completed.

Pennies Results

Dynamic Equilibrium “ The Pennies” Class Results Simulator:

Dynamic Equilibrium “ The Pennies”

Chemical Equilibrium

Reaction Diagram of O 3 decomposing O 3 (g) + O (g) 2 O 2 (g) [breakdown (decomposing)] O 2 (g) + O (g) O 3 (g) [formation]

Chemical Equilibrium  Most of the reactions considered until now have had reactants react completely to form products. These reactions “went” only in one direction. [  ]  Some reactions can react in either direction. They are “reversible”. [ ]When this occurs some amount of reactant(s) will always remain at the end of change. Weak acids and bases follow this type.

Chemical Equilibrium (Definitions)  A chemical system where the concentrations of reactants and products remain constant over time.  On the molecular level, the system is dynamic: The rate of change is the same in both the forward and reverse directions.

Equilibrium Expression **  For any equilibrium Reactants  Products  The Equilibrium Expression relates the concentrations of products and reactants.  The value of the Equilibrium constant, K, indicates which position of equilibrium is favored. K = Reactants Products ___________

Position of Equilibrium  If K is large then there will be a larger concentration of products at equilibrium than of reactants. The position of equilibrium favors products.  If K is small then there will be a larger concentration of reactants at equilibrium than of products. The position of equilibrium favors reactants. K = Reactants Products ___________

 For a reaction: j A + k B l C + m Dj A + k B l C + m D  The law of mass action is represented by the Equilibrium Expression: where K is the Equilibrium Constant. (Units for K will vary.) Law of Mass Action ( The Equilibrium Expression) Law of Mass Action ** ( The Equilibrium Expression)

 Concentration or partial pressure is used.  Concentration of gases depends on the partial pressure of the gas:  (Higher pressure = Higher concentration)  Concentration of solutions depends on the solute to solution ratio (molarity, M). The Equilibrium Expression The Equilibrium Expression **

Equilibrium Expression **  _ NH 3 (g) + _ O 2 (g)  _ NO 2 (g) + _ H 2 O(g)  The following Equilibrium Expression can have the amounts uniformly expressed as units of concentration mol/L (M), or as units of pressure (atm).

Equilibrium Expression **  4 NH 3 (g) + 7 O 2 (g)  4 NO 2 (g) + 6 H 2 O(g)  The following Equilibrium Expression can have the amounts uniformly expressed as units of concentration mol/L (M), or as units of pressure (atm).

Equilibrium Expressions  If a reaction is re-written where the reactants become products and products-reactants, the new Equilibrium Expression is the reciprocal of the old. K new = 1/K original  When the entire equation for a reaction is multiplied by a molar factor n, K new = (K original ) n

Heterogeneous Equilibria  Equilibria that involve more than one phase. CaCO 3 (s)  CaO(s) + CO 2 (g)CaCO 3 (s)  CaO(s) + CO 2 (g) K = [CO 2 ]

Heterogeneous Equilibria  CaCO 3 (s)  CaO(s) + CO 2 (g)CaCO 3 (s)  CaO(s) + CO 2 (g) K = [CO 2 ]  The position of a heterogeneous equilibrium does not depend on the amounts of pure solids or liquids present.

Le Châtelier’s Principle** ... If change is imposed on a system at equilibrium, the system will shift in a direction that tends to reduce that change and re-establish the original equilibrium’s relationship of reactants products.

Le Châtelier’s Principle **

Changes on the System **  1.Concentration: The system will shift concentrations away from the added component. K remains the same.  2.Temperature: K will change depending upon the reaction. If endothermic, heat is a reactant, exothermic, heat is a product. Increasing T will increase or decrease K. Endo  K increases; Exo  K decreases.

Temperature Effects on the NO 2  N 2 O 4 Equilibrium

Changes on the System ** (continued)  3.Pressure: A) Changing the partial pressure of one gas is like changing its concentration It has the same effect as changing the concentration on the position of equilibriumIt has the same effect as changing the concentration on the position of equilibrium  B) Increasing the pressure of the entire system causes the position of equilibrium to shift toward the side of the reaction with the fewer gas molecules. K p = K c (RT)  n  n = n products - n reactants

Changes on the System ** (continued)  3.Pressure: C). Addition of inert gas does not affect the equilibrium position. D). Decreasing the volume of the system increases its pressure shifting the equilibrium toward the side with fewer moles. Reduces the pressure by reducing the total number of gas moleculesReduces the pressure by reducing the total number of gas molecules [ Le Châtelier’s Principle: if pressure is increased the system shifts to minimize the increase.][ Le Châtelier’s Principle: if pressure is increased the system shifts to minimize the increase.]

Changes on the System ** (continued) 4. The Effect of Catalysts  A catalyst lowers the activation energy barrier for any reaction….in both forward and reverse directions!  A catalyst will decrease the time it takes to reach equilibrium.  A catalyst does not effect the composition of the equilibrium mixture.

Reaction Diagram of O 3 decomposing

Catalysts Lower the Energy of Activation O3O3O3O3 O2O2O2O2 with Freon

Catalytic Destruction of Ozone

Satellite Images of the Ozone Hole

Homeostasis Physiological Equilibrium  “Pools, Balance, Equilibrium, Bio-feedback”  Let Pool be a person’s body weight.  Let Input and Output be energy.  (What are possible sources of energy input and forms of energy output?)  Consider a 70 kg individual with Input = Output = 2000 Cal / day, how do you compare?