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Unformatted text preview: 1 Chemical Equilibrium What are the concentrations of reactants and products at equilibrium? How do changes in pressure, volume, temperature, concentration and the use of catalysts affect the equilibrium state? The state of a system at equilibrium is dynamic The rate of the forward reaction is equal to the rate of the reverse reaction. The system hasn’t “stopped” reacting. In chemical kinetics, the focus is on the portion of the reaction prior to t e (the time at which equilibrium is reached). In equilibrium, the focus is on time after which t e occurs. The addition of radioactive NaCl to a saturated solution. Experimental results show that for a given reaction equation at a particular temperature: Given: aA + bB + … ↔ gG + hH + … K c = [G] g [H] h …/[A] a [B] b … This is known as the equilibrium constant equilibrium constant equilibrium constant equilibrium constant expression expression expression expression and K c is called the concentration equilibrium concentration equilibrium concentration equilibrium concentration equilibrium constant constant constant constant (given as a dimensionless quantity) Question 1: Question 1: Question 1: Question 1: Given: CO (g) + Cl 2(g) ↔ COCl 2(g) K c = 1.2x10 3 at 395 o C If [CO] equals [Cl 2 ] at equilibrium for the reaction, is there just one possible value of [COCl 2 ]? Explain. Question 2: Question 2: Question 2: Question 2: Suppose [O 2 ] is fixed at a certain constant value when equilibrium is reached in the following reversible reaction: 2SO 2(g) + O 2(g) ↔ 2SO 3(g) K c = 1.00x10 2 Do [SO 2 ] and [SO 3 ] have unique values? Does the ratio [SO 2 ]/[SO 3 ] have a unique value? Describe the equilibrium state when [O 2 ] = 1.00M. Answers: Question 1: Given: CO (g) + Cl 2(g) ↔ COCl 2(g) K c = 1.2x10 3 at 395 o C If [CO] equals [Cl 2 ] at equilibrium for the reaction, is there just one possible value of [COCl 2 ]? Explain. No. [COCl 2 ] = K c [CO][Cl 2 ], but there are many possible values for [CO]=[Cl 2 ] Question 2: Suppose [O 2 ] is fixed at a certain constant value when equilibrium is reached in the fol owing reversible reaction: 2SO 2(g) + O 2(g) ↔ 2SO 3(g) K c = 1.00x10 2 Do [SO 2 ] and [SO 3 ] have unique values? Does the ratio [SO 2 ]/[SO 3 ] have a unique value? Describe the equilibrium state when [O 2 ] = 1.00M. [SO 2 ] and [SO 3 ] do not have unique values, but the following ratios do: [SO 3 ] 2 /[SO 2 ] 2 ; [SO 2 ] 2 /[SO 3 ] 2 ; [SO 3 ]/[SO 2 ], [SO 2 ]/[SO 3 ]. If [O 2 ] = 1.00M 100 = [SO 3 ] 2 /([O 2 ][SO 2 ] 2 ) 100 = ([SO 3 ]/[SO 2 ]) 2 10 = [SO 3 ]/[SO 2 ] [SO 3 ] = 10[SO 2 ] 2 Equilibrium From the Perspective of Kinetics and Thermodynamics Given 2HI (g) ↔ H 2(g) + I 2(g) And the rate laws are known to be Rate f = k f [HI] 2 Rate r = k r [H 2 ][I 2 ] At equilibrium Rate f = Rate r If the same rate laws govern the reaction at equilibrium: k f [HI] 2 = k r [H 2 ][I 2 ] k f /k r = [H 2 ][I 2 ]/[HI] 2 = K c (the concentration units in k f /k r will match those of K c...
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 Fall '10
 Feebeck
 Equilibrium, Catalyst, Kc

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