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

Equilibrium & KineticsEquilibrium & Kinetics

Dr. Ron RusayDr. Ron Rusay

Summer 2004Summer 2004

© Copyright 2004 R.J. Rusay© Copyright 2004 R.J. Rusay

Dynamic EquilibriumDynamic Equilibrium““The Pennies”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 Keeper1) Money Keeper2) Recorder2) Recorder3) Transfer Agent (Calculating agent)3) Transfer Agent (Calculating agent)4) Auditor (Can be combined with #3)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 After recording all of the names send the Money Keeper to see Dr. R. for your capital stake.to see Dr. R. for your capital stake.• Await instructions for phase I.Await instructions for phase I.


Phase I:Phase I:

Phase II:Phase II:

There will be 8 phases. You can begin and go through them at your own pace. 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 Let Dr. R know when you have completed four phases. Stop at this point. Give

Dr. R. the accounting form when completed.Dr. R. the accounting form when completed.


Class Resultshttp://ep.llnl.gov/msds/chem120/equil-graph.html

Simulator:http://mc2.CChem.Berkeley.EDU/Java/equilibrium/

http://ep.llnl.gov/msds/Chem120/equil-graph.html











http://ep.llnl.gov/msds/chem120/equil-graph.html






Chemical EquilibriumChemical Equilibrium

Reaction Diagram of OReaction Diagram of O33 decomposing decomposing

O3 (g) + O(g) 2 O2 (g) [breakdown (decomposing)]

O2 (g) + O(g) O3 (g) [formation]

Chemical EquilibriumChemical Equilibrium

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

Chemical EquilibriumChemical Equilibrium(Definitions)(Definitions)

A chemical system where the A chemical system where the concentrations of reactants and concentrations of reactants and products remain products remain ________________ over time. over time. On the On the molecular levelmolecular level, the system is , the system is __________: __________: The rate of change is the The rate of change is the ____ in both the forward and reverse ____ in both the forward and reverse directions.directions.

Equilibrium Expression Equilibrium Expression **** For any equilibriumFor any equilibrium

Reactants Reactants ProductsProducts The Equilibrium Expression relates the The Equilibrium Expression relates the

concentrations of products and reactants. concentrations of products and reactants.

The value of the Equilibrium constant, The value of the Equilibrium constant, KK,, indicates indicates which position of equilibrium is favored.which position of equilibrium is favored.

K =K =

Position of EquilibriumPosition of Equilibrium

If K is large then there will be a _______ If K is large then there will be a _______ concentration of products at equilibrium than concentration of products at equilibrium than of reactants. The position of equilibrium of reactants. The position of equilibrium favors _________.favors _________.

If K is _____ then there will be a larger If K is _____ then there will be a larger concentration of reactants at equilibrium than concentration of reactants at equilibrium than of products. The position of equilibrium favors of products. The position of equilibrium favors ___________.___________.

K =K =Reactants

Products ______________________

For a reaction:For a reaction:

• j j A + A + k k B B l l C + C + m m DD The law of mass action is represented The law of mass action is represented

by the Equilibrium Expression: where K by the Equilibrium Expression: where K is the Equilibrium Constant. (Units for K is the Equilibrium Constant. (Units for K will vary.)will vary.)

Law of Mass Action Law of Mass Action ** ((TheThe Equilibrium Expression)Equilibrium Expression)

KK = =

Concentration or partial pressure is used.Concentration or partial pressure is used. Concentration of gases depends on the partial Concentration of gases depends on the partial

pressure of the gas: pressure of the gas: (Higher pressure = Higher concentration)(Higher pressure = Higher concentration) Concentration of solutions depends on the Concentration of solutions depends on the

solute to solution ratio solute to solution ratio (molarity, M).(molarity, M).Klmjk=CDABThe Equilibrium ExpressionThe Equilibrium Expression **

Equilibrium Expression Equilibrium Expression **** _ _ NHNH33(g) + (g) + _ _ OO22(g) (g) _ _ NONO22(g) + (g) + __HH22O(g)O(g) The following Equilibrium Expression can have the The following Equilibrium Expression can have the

amounts uniformly expressed as units of amounts uniformly expressed as units of concentration mol/L (M), or as units of pressure concentration mol/L (M), or as units of pressure (atm).(atm).

Equilibrium ExpressionsEquilibrium Expressions

If a reaction is re-written where the If a reaction is re-written where the reactants become products and reactants become products and products-reactants, the new Equilibrium products-reactants, the new Equilibrium Expression is the reciprocal of the old. Expression is the reciprocal of the old.

KKnewnew = = When the entire equation for a reaction When the entire equation for a reaction

is multiplied by a molar factor is multiplied by a molar factor nn, , KKnewnew = =

Heterogeneous EquilibriaHeterogeneous Equilibria Equilibria that involve more than one Equilibria that involve more than one phase.phase.

• CaCOCaCO33(s) (s) CaO(s) + CO CaO(s) + CO22(g)(g)

Heterogeneous EquilibriaHeterogeneous Equilibria

• CaCOCaCO33(s) (s) CaO(s) + CO CaO(s) + CO22(g)(g)

K = K =

The position of a heterogeneous The position of a heterogeneous equilibrium equilibrium __________________________________ on the on the amounts of amounts of pure solidspure solids or or liquids liquids present.present.

Le Châtelier’s PrincipleLe Châtelier’s Principle****

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

Le Châtelier’s Principle Le Châtelier’s Principle ****

Changes on the System Changes on the System ****

1.1. ConcentrationConcentration: The system will shift : The system will shift concentrations concentrations ____________ from the added from the added component. component. K remains the sameK remains the same..

2.2. TemperatureTemperature: K will change : K will change depending upon the reaction. If endothermic, depending upon the reaction. If endothermic, heat is a reactant, exothermic, heat is a heat is a reactant, exothermic, heat is a product. Increasing T will increase or product. Increasing T will increase or decrease K. decrease K. Endo Endo K _________; Exo K _________; Exo K ________.K ________.

Temperature Effects onTemperature Effects onthe NOthe NO22 N N22OO44 Equilibrium Equilibrium

Changes on the System Changes on the System **** (continued)(continued)

3.3. PressurePressure: : A) A) Changing the partial pressure of one Changing the partial pressure of one gas is like changing its concentrationgas is like changing its concentration• It has the same effect as changing the It has the same effect as changing the

concentration on the position of equilibriumconcentration on the position of equilibrium B) Increasing the pressure of the entire B) Increasing the pressure of the entire

system causes the position of equilibrium system causes the position of equilibrium to shift toward the side of the reaction with to shift toward the side of the reaction with the fewer gas molecules.the fewer gas molecules.

Kp = Kc (RT)n


3.3. PressurePressure: : C). Addition of inert gas C). Addition of inert gas ___________ ___________ the the

equilibrium position.equilibrium position.

D). Decreasing the volume of the system D). Decreasing the volume of the system ______________ its pressure______________ its pressure shifting the shifting the equilibrium toward the side with fewer equilibrium toward the side with fewer moles.moles.• Reduces the pressure by reducing the total Reduces the pressure by reducing the total

number of gas moleculesnumber of gas molecules

• [[Le Châtelier’s PrincipleLe Châtelier’s Principle: if pressure is increased the : if pressure is increased the system shifts to minimize the increase.]system shifts to minimize the increase.]


4.4. The Effect of Catalysts The Effect of Catalysts A catalyst lowers the activation energy barrier A catalyst lowers the activation energy barrier

for any reaction….in both forward and reverse for any reaction….in both forward and reverse directions!directions!

A catalyst will decrease the time it takes to A catalyst will decrease the time it takes to reach equilibrium.reach equilibrium.

A catalyst A catalyst ________________ effect the composition of effect the composition of the equilibrium mixture.the equilibrium mixture.

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Catalysts Lower the Energy of ActivationCatalysts Lower the Energy of Activation

OO33

OO22

with Freonwith Freon

Catalytic Destruction of OzoneCatalytic Destruction of Ozone

Satellite Images of the Ozone Satellite Images of the Ozone HoleHole

Documents

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