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2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006 Introduction to Equilibrium Concepts John I. Gelder Former Chief Reader AP Chemistry Department of Chemistry Oklahoma State University

2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

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2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006. Introduction to Equilibrium Concepts John I. Gelder Former Chief Reader AP Chemistry Department of Chemistry Oklahoma State University. Important Web Site. - PowerPoint PPT Presentation

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Page 1: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

2-Day AP/Pre-AP Science ConferenceCorpus Christi Omni-Marina Hotel

January 20 & 21, 2006

Introduction to Equilibrium Concepts

John I. Gelder

Former Chief Reader AP Chemistry

Department of Chemistry

Oklahoma State University

Page 2: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Important Web SiteParticulate Level Simulations (Supported by the

National Science Foundation)http://genchem1.chem.okstate.edu/CCLI/Startup.htmlLoginFree access to simulations and guided inquiry

activities.

Gas LawsShifting Reactions (Equilibrium)Chemical Kinetics

Page 3: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisCharacteristics of a hypothetical chemical reaction?

Investigate the reaction: R + GB

Investigate the reaction: B + RG

Reversible reaction

Irreversible reaction

Page 4: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisHow can concentration changes affect a

chemical reaction?

Experiment #1:Experiment #2: Add reactant R (to 2.0 M)Experiment #3: Add reactant BG (to 2.0 M)Experiment #4: Remove reactants R and BG (to 1.0 and

0.8 M)Experiment #5: Add product RG (to 1.5 M) PredictExperiment #6: Remove product RG (to 0.5 M)) Predict

Page 5: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental Basis

How can concentration changes affect a chemical reaction?

Summary of Data

Exp. Stress

Change in [reactants]

Change in [products] Reaction Shifts

#2 Add R Conc decrease

Conc. Increases

Left to right

#3

#4….

Page 6: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental Basis

How can concentration changes affect a chemical reaction?

Review the summary of your experimental observations and write a statement(s) that generalizes how stressing a reaction by adding or removing a reactant of product shifts the chemical reaction.

Page 7: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisWhat is the relationship between reactant and product

concentrations at the end of a chemical reaction?

Exp. Initial Conditions Final Conditions

R BG RG B R BG RG B

#1 2.0 2.0 0 0

#2 1.0 1.0 0 0

#3 1.5 1.5 0 0

#4 0 0 1.0 1.0

#6 1.0 0.6 1.2 0.8

Page 8: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisWhat is the relationship between reactant and product

concentrations at the end of a chemical reaction?

Exp. Initial Conditions Final Conditions

R BG RG B R BG RG B

#1 2.0 2.0 0 0 .64 .64 1.36 1.36

#2 1.0 1.0 0 0

#3 1.5 1.5 0 0

#4 0 0 1.0 1.0

#6 1.0 0.6 1.2 0.8

Page 9: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisWhat is the relationship between reactant and product

concentrations at the end of a chemical reaction?

Exp. Initial Conditions Final Conditions

R BG RG B R BG RG B

#1 2.0 2.0 0 0 .64 .64 1.36 1.36

#2 1.0 1.0 0 0 .32 .32 0.68 0.68

#3 1.5 1.5 0 0

#4 0 0 1.0 1.0

#6 1.0 0.6 1.2 0.8

Page 10: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisWhat is the relationship between reactant and product

concentrations at the end of a chemical reaction?

Exp. Initial Conditions Final Conditions

R BG RG B R BG RG B

#1 2.0 2.0 0 0 .64 .64 1.36 1.36

#2 1.0 1.0 0 0 .32 .32 0.68 0.68

#3 1.5 1.5 0 0 .48 .48 1.02 1.02

#4 0 0 1.0 1.0

#6 1.0 0.6 1.2 0.8

Page 11: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisWhat is the relationship between reactant and product

concentrations at the end of a chemical reaction?

Exp. Initial Conditions Final Conditions

R BG RG B R BG RG B

#1 2.0 2.0 0 0 .64 .64 1.36 1.36

#2 1.0 1.0 0 0 .32 .32 0.68 0.68

#3 1.5 1.5 0 0 .48 .48 1.02 1.02

#4 0 0 1.0 1.0 .32 .32 0.68 0.68

#6 1.0 0.6 1.2 0.8

Page 12: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental BasisWhat is the relationship between reactant and product

concentrations at the end of a chemical reaction?

Exp. Initial Conditions Final Conditions

R BG RG B R BG RG B

#1 2.0 2.0 0 0 .64 .64 1.36 1.36

#2 1.0 1.0 0 0 .32 .32 0.68 0.68

#3 1.5 1.5 0 0 .48 .48 1.02 1.02

#4 0 0 1.0 1.0 .32 .32 0.68 0.68

#6 1.0 0.6 1.2 0.8 .79 .39 1.41 1.01

Page 13: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental Basis

What is the relationship between reactant and product concentrations at the end of a chemical reaction?

Challenge students to arrive at an algebraic equation that relates the concentrations of the reactants and products in the reaction. Hints….

Use the results to predict the final concentrations for a new initial set of conditions.

Page 14: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Experimental Basis

Additional Investigations:Try some different reactions: R + G RG

BG B + GRB R + B

Change in temperature;Change the volume of the container;K, T and ∆HK and Q

Page 15: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Introduction to Equilibrium

K, the equilibrium constant, measures the extent of a chemical reaction.

Large K (greater than 1) reaction will proceed towards products when the initial conditions have all reactants and products at 1 M or 1 atm.

Small K (less than 1) reaction will proceed towards reactants when the initial conditions have all reactants and products at 1 M or 1 atm.

Page 16: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

Introduction to Equilibrium

aA(g) + bB(g) cC(g) + dD(g)

Kp = PcC · Pd

D/PaA · Pb

B

KC = [C]c · [D]d/ [A]a · [B]b

Kp = KC·(RT)∆n

Page 17: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2000K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2] = 0.20 mol/L

[CO2] = 0.30 mol/L

[H2O] = [CO] = 0.55 mol/La) What is the mol fraction of CO(g) in the equilibrium mixture?b) Using the equilibrium concentrations given above, calculate the value of

KC, the equilibrium constant for the reaction.

c) Determine KP in terms KC of for the system.d) When the system is cooled from 2000 K to a lower temperature, 30.0%

of the CO(g) is converted back to CO2(g). Calculate the value of KC at this lower temperature.

e) 0.50 mol of H2 is mixed with 0.50 mol of CO2 in a 3.0 liter container at 2000 K. Calculate the CO(g) at equilibrium.

Page 18: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2000K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2] = 0.20 mol/L

[CO2] = 0.30 mol/L

[H2O] = [CO] = 0.55 mol/La) What is the mol fraction of CO(g) in the equilibrium

mixture?Mol fraction CO = mol CO/total mol = 0.55/1.60

= 0.34

Page 19: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2000K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2] = 0.20 mol/L

[CO2] = 0.30 mol/L

[H2O] = [CO] = 0.55 mol/L

b) Using the equilibrium concentrations given above, calculate the value of KC, the equilibrium constant for the reaction.

KC = [H2O] · [CO]/ [H2] · [CO2]= [0.55] · [0.55]/ [0.20] · [0.30]

= 5.0

Page 20: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2000K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2] = 0.20 mol/L

[CO2] = 0.30 mol/L

[H2O] = [CO] = 0.55 mol/L

c) Determine KP in terms KC of for the system.

Kp = KC·(RT)∆n

∆n = mol product gases - mol of reactant gases∆n = 1 + 1 - (1 + 1) = 0

Kp = KC

Page 21: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2000K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2] = 0.20 mol/L

[CO2] = 0.30 mol/L

[H2O] = [CO] = 0.55 mol/L

d) When the system is cooled from 2000 K to a lower temperature, 30.0% of the CO(g) is converted back to CO2(g). Calculate the value of KC at this lower temperature.

Page 22: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

initial 0.20 0.30 0.55 0.55change - 0.17 equilibrium

0.30 · 0.55 M = 0.17 M0.17 M CO reacts

Page 23: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

initial 0.20 0.30 0.55 0.55change + 0.17 + 0.17 - 0.17 - 0.17 equilibrium 0.37 0.47 0.38 0.38

KC = [H2O] · [CO]/ [H2] · [CO2]= [0.38] · [0.38]/ [0.37] · [0.47]

= 0.83

Page 24: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2000K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2] = 0.20 mol/L

[CO2] = 0.30 mol/L

[H2O] = [CO] = 0.55 mol/L

e) 0.50 mol of H2 is mixed with 0.50 mol of CO2 in a 3.0 liter container at 2000 K. Calculate the CO(g) at equilibrium.

Page 25: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

e) 0.50 mol of H2 is mixed with 0.50 mol of CO2 in a 3.0 liter container at 2000 K. Calculate the CO(g) at equilibrium.

[H2] = [CO2] = 0.50 mol/3.0 L = 0.17 M

Page 26: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

initial 0.17 0.17 0 0changeequilibrium

Q = [H2O] · [CO]/ [H2] · [CO2]= [0] · [0]/ [0.17] · [0.17]

= 0

So Q < Kc (5.0)So the reaction proceeds from left to right to establish equilibrium

Page 27: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1995 H2(g) + CO2(g) H2O(g) + CO(g)

initial 0.17 0.17 0 0change -x -x +x +xequilibrium 0.17 - x 0.17 - x 0 - x 0 - x

Kc = [H2O] · [CO]/ [H2] · [CO2]5.0 = [x] · [x]/ [0.17 - x] · [0.17 - x]

5.0 = x2/(0.17 - x)2

2.236 = x/(0.17 - x)x = 0.12 M = [CO]

Page 28: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1998 C(s) + H2O(g) CO(g) + H2(g) Hº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement.

• Additional H2(g) is added to the equilibrium mixture at constant volume.

• The temperature of the equilibrium mixture is increased at constant volume.

• The volume of the container is decreased at constant temperature.

(d) The graphite pellets are pulverized.

Page 29: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1998 C(s) + H2O(g) CO(g) + H2(g) Hº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement.

• Additional H2(g) is added to the equilibrium mixture at constant volume.

• The temperature of the equilibrium mixture is increased at constant volume.

• The volume of the container is decreased at constant temperature.(d) The graphite pellets are pulverized.

Kp = PCO · PH2/PH2O

Page 30: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1998 C(s) + H2O(g) CO(g) + H2(g) Hº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement.

• Additional H2(g) is added to the equilibrium mixture at constant volume.

Kp = PCO · PH2/PH2O

Adding H2(g) causes Q to be greater than Kp.

The reaction must shift in the direction to reduce Q, right to left. The moles of CO(g) will decrease.

Page 31: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1998 C(s) + H2O(g) CO(g) + H2(g) Hº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement.

(b) The temperature of the equilibrium mixture is increased at constant volume.

The reaction is endothermic. Increasing the temperature corresponds to adding heat to the reactants side. The reaction will shift from left to right to relieve the

stress. The moles of CO(g) will increase.

Page 32: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1998 C(s) + H2O(g) CO(g) + H2(g) Hº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement.

(c ) The volume of the container is decreased at constant temperature.

Decreasing the volume of the container, increases the pressure inside, to relieve the pressure the reaction will proceed in the direction to decrease the pressure (in the

direcction of the fewest moles of gas) the reaction will proceed from right to left. The moles of CO(g) will decrease.

Page 33: 2-Day AP/Pre-AP Science Conference Corpus Christi Omni-Marina Hotel January 20 & 21, 2006

1998 C(s) + H2O(g) CO(g) + H2(g) Hº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement.

(d) The graphite pellets are pulverized.

Kp = PCO · PH2/PH2O

Since C(s) does not appear in the equilibrium expression pulverizing the graphite has no effect of the moles of CO(g).

So the moles of CO(g) remain the same.