IB Chemistry on Dynamic Equilibrium and Equilibrium Constant
Gaseous Chemical Equilibrium. The Dynamic Nature of Equilibrium A. What is equilibrium? a state of...
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Transcript of Gaseous Chemical Equilibrium. The Dynamic Nature of Equilibrium A. What is equilibrium? a state of...
![Page 1: Gaseous Chemical Equilibrium. The Dynamic Nature of Equilibrium A. What is equilibrium? a state of balance; no net change in a dynamic process.](https://reader035.fdocuments.net/reader035/viewer/2022062413/5a4d1b697f8b9ab0599b2361/html5/thumbnails/1.jpg)
Gaseous Chemical Equilibrium
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The Dynamic Nature of Equilibrium
A. What is equilibrium?• a state of balance; no net change in a dynamic process
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1. Chemical equilibrium
No net change with the total amount of reactants and products remaining constant, while the reaction continues
Eek = equilibrium
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2. General Characteristics• Double Headed Arrow • Beginning of Rxn Form lots of products (before eek
is established)• Moments Later Forming both products and
reactants (eek)• **Not Necessarily equal proportions of both sides of
the reaction!
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B. Dynamic Equilibrium - Characteristics • two opposing processes occur at exactly the same rate• No net change• Dynamic Eek will not occur as soon as the reversible
reaction begins, it takes time.
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C. Graph
The N2O4 2NO2 Equilibrium System
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D. The 2NO2N2O4 Equilibrium System
1. Description• Dynamic, reversible, no net change
2. Equilibrium Conditions• Specific for a Reaction (will be unique)
• MUST have the Balanced Written Equation• Coefficients will matter!
• Temperature Dependent• CONSTANT regardless of concentration
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II. The Equilibrium Expression, Keq(Equilibrium Law or Law of Mass-Action)
A. Writing Expressions for Keq
• aA + bB <-----> cC + dD
• Keq = [C]c [D]d _ for aqueous solutions use
[A]a [B]b Molarities
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The Equilibrium Expression
Example: Write the Keq for:• 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
• N2(g) + 3H2(g) 2NH3(g)
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B. Characteristics of Keq
1. Independent of :• Pure solids and pure liquids as long as some of the
substance is present2. Dependent on:• Gaseous substances and solutions (aqueous)
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C. The meaning of Keq
1. Keq = 1; reactants and products are present in equal amounts at eek
2. Keq > 1; products are present in greater proportion at eek
3. Keq < 1; reactants are present in greater proportion at eek
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4. Examples:
N2(g) + O2(g) 2 NO(g) Keq=55
N2(g) + 3H2(g) 2NH3(g) Keq=5x10-6
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III. Modifying Equilibrium Constant Expressions
A. Reversible reactions1. Rule:• The Keq value for the reverse of a reaction will be
the reciprocal
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III. Modifying Equilibrium Constant Expressions
Example: write the Keq for the following equation and its reverse
A(g) + B(g) C(g)
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III. Modifying Equilibrium Constant Expressions
B. Summation of Reactions and modifying coefficientsRule:
the Keq of summed reactions will be the product of the Keq’s; the factor you adjust coefficients by becomes the power
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Example:
A(g) + B(g) C(g) Keq=3A(g) + B(g) D(g) Keq=6What is the Keq for C(g) D(g)
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Example:
½ N2(g) +1/2O2(g) NO(g) Keq=6.9x10-16
NO2(g) NO(g) + ½ O2(g) Keq=6.7x10-7
N2O4(g) 2NO2(g) Keq=0.15
What is the Keq for N2(g)+2O2(g)N2O4(g)
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C. Heterogeneous SystemsRule: solid and liquid substances = 1
Example: Write the Keq for:
Zn(s) + 2H+(aq) Zn2+
(aq) + H2(g)
CaCO3(s) CaO(s) + CO2(g)
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IV. Determination of KA. Calculating Keq from experimental values.
Write the expression for the reversible reaction between solid ammonium chloride and gaseous products, hydrogen chloride and ammonia (NH3). At equilibrium in a 1 liter container, the following amounts are present: 12.0 mol ammonium chloride, 3.0 mol of ammonia and 5.0 mol of hydrogen chloride Determine the Keq.
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B. Example When 4.29 moles of PCl3(g) and 4.29 moles of Cl2(g) are placed in a 1.00 Liter container at 250oC, the following equilibrium is established:
PCl3(g) + Cl2(g) PCl5(g)The equilibrium concentration of phosphorus pentachloride is 2.59 mol/L. What are the equilibrium concentrations of the other two gases? Calculate Keq for the above reaction system.
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C. Example: Consider the equilibrium system: 2NO(g) + Br2(g) 2NOBr(g)
At a given temperature, 1.6 mol of NO and 1.6 mol of Br2 are added to a 1.00 Liter flask and the equilibrium concentration of NOBr is found to be 0.53 M. Calculate the equilibrium concentrations of the other 2 gases and the value of Keq.
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B. IRE Problems with unknown equilibrium concentrations
Description of problems• Define both the R and E lines in terms of “x”
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2. Example: Carbon dioxide and hydrogen gas at concentrations of 1.00 M each are introduced into a container and the following system is established: CO2(g) + H2(g) CO(g) + H2O(g) Kc = 0.64 What are the equilibrium concentrations of all the species?
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3. Example: For the system: H2(g) + I2(g) 2HI(g) at 425 oC, K = 55.5. If 2.5 atm of hydrogen and 2.5 atm of iodine are placed in a vessel and heated to 425oC and the system reaches equilibrium, what are the pressures of all species?
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
A. Statement of Le Chatelier’s Principle
“When a system is stressed (changes in concentration, temp,
gas pressure, or volume of container), the system will respond by attaining new equilibrium conditions that
counteract the change”
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
B. For the system, N2O4(g) 2NO2(g) H = 57.2 kJ
1. Changes in amounts of speciesa. Adding or removing reactant
• Add Reactant Eek shifts toward products (use it up)
• Remove Reactant Eek shifts toward reactants (make more)
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
b. Adding or removing product• Add Product Eek shifts toward reactants (use it up) • Remove Product Eek shifts toward products (make
more)
c. Adding or removing pure solid or solvent• Has NO effect on equilibrium (no shift)
d. Adding inert substance (inert = non-reactive)• Has NO effect on equilibrium (no shift)
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
2. Changes in pressure• Pressure increased Eek shifts in the direction producing
the smaller number of moles of gas
• Pressure decreased Eek shifts in the direction producing the larger number of moles of gas
• Moles of gas equal on both sides = pressure does not effect Eek.
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
3. Changes in volume• Decreases in volume = increase in pressure• Increases in volume = decrease in pressure
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
4. Changes in temperature • Increase Temp Eek shifts in the direction of the
endothermic rxn; away from heat
• Decrease Temp Eek shifts in the direction of the exothermic rxn; toward heat
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
Example 14.12 List all of the ways to shift the equilibrium of the following systems to the right:
a. N2(g) + 3H2(g) 2NH3(g)
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14.4 Qualitative Treatment of Equilibrium: Le Chatelier
b. CO(g) + H2O(g) CO2(g) + H2(g)
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End of Chapter 14!