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Equilibrium Chapter 15 Chemical Equilibrium

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Equilibrium What is a chemical equilibrium? The reaction of hemoglobin with oxygen is a reversible reaction.

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Equilibrium If the forward and reverse rxns move at the same speed we combine both rxns and represent it like this:

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Equilibrium High Altitude Training Increases The Concentration of Hemoglobin An Altitude or Hypoxic Tent

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Equilibrium

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An Altitude Training Tent for Dogs

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Equilibrium What is chemical equilibrium?

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Equilibrium Assuming the forward and reverse rxns are elementary, then the hemoglobin reaction can be defined in terms of chemical kinetics.

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Equilibrium We can show for a reversible rxn having equal rates in both directions that….

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Equilibrium What is a chemical equilibrium? A chemical equilibrium is a reversible reaction where the rate fwd = rate rev

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Equilibrium

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Note: The reactant and product concentrations do not change when a reaction is at equilibrium. What is the equilibrium concentration of the product? What is the equilibrium concentration of the reactant?

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Equilibrium Note: The reactant and product concentrations are not equal when a reaction is at equilibrium but ….. but … but two or more reactants or two or more products can have equal but constant equilibrium concentrations.

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Equilibrium Writing Equilibrium Constant-Expressions

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Equilibrium The equilibrium constant expression is the ratio of product concentrations to reactant concentrations. K c = [C] c [D] d [ A] a [B] b aA + bBcC + dD

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Equilibrium

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The Equilibrium Constant The equilibrium expression can also be written in terms of pressure when the expression contain only gases.

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Equilibrium Recall how K c is derived

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Equilibrium Equilibrium Constant Expression Workshop

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Equilibrium Relationship between K c and K p Using the Ideal Gas Law (PV = nRT) we can show derive and equation relating K p and K c and K p. where K p = K c (RT) n n = (moles of gaseous product) − (moles of gaseous reactant )

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Equilibrium Calculating Equilibrium Concentrations (Using the equilibrium expression to determine [ ] eq

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Equilibrium Equilibrium Calculation Workshop Calculate the [ ] eqs for this reaction. The K c is 0.110 and 0.500 mol of ICl was placed in a 5.00-L flask.

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Equilibrium Organize the process from beginning to end. Step I. Write the equilibrium expression Step II. Express the unknown [ ]eqs in terms of x and the respective initial concentrations ( constructing a table is helpful) Step III. Substitute the unknown [ ]eqs and K c in the equilibrium expression and solve for x

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Equilibrium Practice Problem 15-6 Calculate the [ ] eqs for this reaction. The K c is 5.10 at 700K and 1.000 mol of each compound was placed in a 1.000-L flask.

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Equilibrium Equilibrium Calculations A system initially contains 1.000 x 10 −3 M H 2 and 2.000 x 10 −3 M I 2 and is allowed to reach equilibrium. The concentration of HI in the equilibrium mixture is 1.87 x 10 −3 M. What is K c at 448 C for the reaction shown below. H 2 (g) + I 2 (g) 2 HI (g)

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Equilibrium What Do We Know? [H 2 ], M[I 2 ], M[HI], M Initially1.000 x 10 -3 2.000 x 10 -3 0 Change At equilibrium 1.87 x 10 -3

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Equilibrium [HI] Increases by 1.87 x 10 -3 M [H 2 ], M[I 2 ], M[HI], M Initially1.000 x 10 -3 2.000 x 10 -3 0 Change+1.87 x 10 -3 At equilibrium 1.87 x 10 -3

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Equilibrium Stoichiometry tells us [H 2 ] and [I 2 ] decrease by half as much [H 2 ], M[I 2 ], M[HI], M Initially1.000 x 10 -3 2.000 x 10 -3 0 Change-9.35 x 10 -4 +1.87 x 10 -3 At equilibrium 1.87 x 10 -3

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Equilibrium We can now calculate the equilibrium concentrations of all three compounds… [H 2 ], M[I 2 ], M[HI], M Initially1.000 x 10 -3 2.000 x 10 -3 0 Change-9.35 x 10 -4 +1.87 x 10 -3 At equilibrium 6.5 x 10 -5 1.065 x 10 -3 1.87 x 10 -3

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Equilibrium …and, therefore, the equilibrium constant Kc =Kc = [HI] 2 [H 2 ] [I 2 ] = 51 = (1.87 x 10 -3 ) 2 (6.5 x 10 -5 )(1.065 x 10 -3 )

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Equilibrium Equilibrium Can Be Reached from Either Direction As you can see, the ratio of [NO 2 ] 2 to [N 2 O 4 ] remains constant at this temperature no matter what the initial concentrations of NO 2 and N 2 O 4 are.

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Equilibrium Equilibrium Can Be Reached from Either Direction This is the data from the last two trials from the table on the previous slide.

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Equilibrium Equilibrium Can Be Reached from Either Direction It does not matter whether we start with N 2 and H 2 or whether we start with NH 3. We will have the same proportions of all three substances at equilibrium.

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Equilibrium Equilibrium Position

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Equilibrium The size of K is an indication of the equilibrium position. Equilibrium position is the side of the reaction the equilibrium favors terms of reactants and products. If K >> 1, the reaction is product-favored; or the equilibrium lies to the right.

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Equilibrium If K << 1, the reaction is reactant-favored; the equilibrium lies to the left.

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Equilibrium Heterogeneous Equilibria

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Equilibrium Pure solids and pure liquids are not included in Kc expressions for heterogeneous equilibria What is the equilibrium-constant expression for this reaction? K c = [Pb 2+ ] [Cl − ] 2

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Equilibrium

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The Reaction Quotient, Q c

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Equilibrium The Reaction Quotient (Q) The reaction quotient is a ratio of nonequilibrium or initial reactant and product concentrations. Q is used to predict the direction a reaction will take in order to reach equilibrium.

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Equilibrium The Reaction Quotient (Q) To do this we must: (1) calculate Q from the initial concentrations and (2) compare Q to K. There are three possibilities: Q = K, Q K

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Equilibrium If Q = K means the reaction is at equilibrium and Change is required in [product] or [reactant]

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Equilibrium Q < K means that [products] must be increased for the reaction to attain equilibrium Q < K, equilibrium shifts right

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Equilibrium Q > K, equilibrium shifts left Q > K means that [products] must be decreased for the reaction to attain equilibrium.

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Equilibrium Q c = [C] c [D] d [ A] a [B] b Q is calculated the same as K except only initial concentrations can be used in the reaction quotient expression.

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Equilibrium Le Châtelier’s Principle

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Equilibrium Le Châtelier’s Principle Le Châtelier’s principle states: a chemical equilibrium will shift left or shift right to counteract a change that disturbs the equilibrium.

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Equilibrium What Happens When More of a Reactant Is Added to a System?

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Equilibrium The Haber Process The transformation of nitrogen and hydrogen into ammonia (NH 3 ) is of tremendous significance in agriculture, where ammonia-based fertilizers are of utmost importance.

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Equilibrium Effect of Pressure

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Equilibrium The Haber Process

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Equilibrium Effect of Temperature pinkblue ∆H > 0 Reaction is placed in a hot water bath

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Equilibrium Effect of Temperature pinkblue ∆H > 0 Reaction is placed in a ice-water bath

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Equilibrium A catalyst does not affect the equilibrium position Effect of Catalysts

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Equilibrium

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Which reaction does not represent a chemical equilibrium?

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Equilibrium Manipulating Equilibrium Constants The equilibrium constant of a reaction in the reverse reaction is the reciprocal of the equilibrium constant of the forward reaction. 1 0.212 = K c = = 0.212 at 100 C [NO 2 ] 2 [N 2 O 4 ] N2O4 (g)N2O4 (g) 2 NO 2 (g) K c = = 4.72 at 100 C [N 2 O 4 ] [NO 2 ] 2 N2O4 (g)N2O4 (g) 2 NO 2 (g)

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Equilibrium Manipulating Equilibrium Constants The equilibrium constant of a reaction that has been multiplied by a number is the equilibrium constant raised to a power that is equal to that number. K c = = 0.212 at 100 C [NO 2 ] 2 [N 2 O 4 ] N2O4 (g)N2O4 (g) 2 NO 2 (g) K c = = (0.212) 2 at 100 C [NO 2 ] 4 [N 2 O 4 ] 2 2 N 2 O 4 (g) 4 NO 2 (g)

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Equilibrium Manipulating Equilibrium Constants The equilibrium constant for a net reaction made up of two or more steps is the product of the equilibrium constants for the individual steps.

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