Chemical Equilibrium 1.Dynamic Equilibrium 2.Physical and Chemical Equilibrium 3.Equilibrium...

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Transcript of Chemical Equilibrium 1.Dynamic Equilibrium 2.Physical and Chemical Equilibrium 3.Equilibrium...

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Chemical EquilibriumDynamic EquilibriumPhysical and Chemical EquilibriumEquilibrium Constant ExpressionFactors Affecting EquilibriumTable of Contents1ReactionsIrreversibleReversibleThe one goes completion.Explosions, burningprocesses, decay of leaves, etc.The one that can occur in boththe forward and the reversedirections. Formation of NH3 , HCl, H2SO4. Chemical Equilibrium2Dynamic Equilibrium

Consider this process,H2O(l) H2O(g) rate of vaporization = rate of condensation The amounts of water vapor and liquid water remain constant. Evaporation and condensation continues on microscopic scale. This is called dynamic equilibrium. Equilibrium is a state in which there are no observable changes as time goes by.31. Physical Equilibrium An equilibrium established by changing states of matter is called physical equilibrium.H2O(l) H2O(g)

4Chemical equilibrium is achieved when:the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constantChemical equilibrium 14.1

Chemical Equilibrium

Chemical Equilibrium2. Chemical EquilibriumFundamentals of Dynamic EquilibriumIt does not show any visible change.It reaches through spontaneous change.Forward and reverse reactions take place continuously.It must be in a closed system.Temperature must be kept constant through equilibrium.Example 1H2(g) + Cl2(g) 2HCl(g) (homogeneous) Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) (heterogeneous)2. Chemical Equilibrium3. Equilibrium Constant Expression

Chapter 34. Equilibrium Constant Expression3. Equilibrium Constant Expression Solid and liquid substances are not included in Kc expressions. Example 1Write Kc expressions of the following equilibrium reactions.N2H4(g) 2NO2(g)2Mg(s) + O2(g) 2MgO(s)2NH3(g) N2(g) + 3H2(g)Ag+(aq) + Cl-(aq) AgCl(s)

Solution3. Equilibrium Constant ExpressionExample 2The following reaction is allowed to reach equilibrium. X2(g) + 2Y2(g) 2XY2(g) The initial amounts of X2 and Y2 gas present in a 2-L container are 2 mol and 6 mol respectively. The amount of XY2 is 1 mol at equilibrium. What is the value of equilibrium constant Kc? 3. Equilibrium Constant ExpressionSolutionX2(g) + 2Y2(g) 2XY2(g) Initial:2 mol 6 mol -Change: -0.5 mol -1 mol + 1 molAt equilibrium:1.5 mol 5 mol 1 mol

Concentrations: 1.5/2 M 5/2 M M0.75 M 2.5 M 0.5 M 3. Equilibrium Constant ExpressionExample 3A 0.80 g sample of SO3 placed in a 1.00 liter container decomposes 80% to establish equilibrium represented by the equation 2SO3(g) 2SO2(g) + O2(g) at 1100 K. Calculate Kc for this reaction. (S:32, O:16)3. Equilibrium Constant ExpressionSolution 2SO3(g) 2SO2(g) + O2(g) Initial: 0.01 mol - - Change: - 0.008 mol +0.008 mol + 0.004 mol At equilibrium 0.002 mol 0.008 mol 0.004 mol

Concentrations 0.002/1 M 0.008/1 M 0.004/1 Mni = 0.8/80= 0.01 mol neq= 0.01 0.01x0.80 (80%decomposes) = 0.002 mol 3. Equilibrium Constant ExpressionaA(g) + bB(g) cC(g) + dD(g)Kp = Kc (RT)nThe relation Between Kp and KcWhere n = (c + d) (a+b)If n = 0, then Kp = Kc Example 10Find Kp and Kc relationship for the reaction below.2CO(g) + O2(g) 2CO2(g)SolutionKp = Kc (RT)2-(2+1) Kp = Kc (RT)-13. Equilibrium Constant ExpressionExample 4Find Kp and Kc relationship for the reactions below.H2(g) + I2(g) 2HI(g)C(s) + H2O(g) CO(g) + H2(g)CO(g) + H2(g) CH3OH(g)N2O4(g) 2NO2(g)Example 54 moles of NH3 in a 2-L vessel is allowed to come equilibrium at a total pressure of 3.6 atm. The number of mole of N2(g) in the equilibrium mixture is measured to be 1 mol. What is the Kp for the following reaction below? 2NH3(g) N2(g) + 3H2(g) 3. Equilibrium Constant ExpressionSolution 2NH3(g) N2(g) + 3H2(g) Initial: 4 mol - - Change: -2 mol +1 mol +3 mol At equilibrium: 2 mol 1 mol 3 molConcentrations: 2/2 M M 3/2 M PV = ntRT 3.6x2 = 6xRT RT = 1.2

Kp = Kc(RT)n Kp = 1.6875(1.2)(1+3) -2 = 2.433. Equilibrium Constant ExpressionThe value of Kc changes by altering the reaction in different ways.Variation of Kc ExpressionThe equilibrium constant for the forward and reversereactions are the reciprocal of each other. 2CO(g) + O2(g) 2CO2(g)Kc For the reverse reaction; 2CO2(g) 2CO(g) + O2(g)

3. Equilibrium Constant ExpressionIf the coefficient of a reaction equation are multiplied by anumber; the equilibrium constant is raised to the power of thatnumber.2CO(g) + O2(g) 2CO2(g)Kc For the reaction; 4CO(g) + 2O2(g) 4CO2 (g)

3. Equilibrium Constant ExpressionIf a reaction equation is expressed as a sum of two or more reaction equations, Kc for the overall reaction is the product of the equilibrium constants of individual reactions. CO2(g) CO(g) + 1/2O2(g) Kc1 H2(g) + 1/2O2(g) H2O(g) Kc2 H2(g) + CO2(g) H2O(g) + CO(g) Kc = Kc1 x Kc2

3. Equilibrium Constant ExpressionExample 6Suppose that the Kc for the reaction below is 4 at a certaintemperature.A2(g) + 1/2B2(g) A2B(g)

2A2(g) + B2(g) 2A2B(g)3A2B(g) 3A2(g) + 3/2B2(g)1/2A2B(g) 1/2A2(g) +1/4B2(g)3. Equilibrium Constant ExpressionSolutionA2(g) + 1/2B2(g) A2B(g)Kc = 4

2A2(g) + B2(g) 2A2B(g) Kc` = (Kc)2 = 42 = 163A2B(g) 3A2(g) + 3/2B2(g) Kc` = (1/Kc)3 = ()3 = 1/64 = 0.0156 1/2A2B(g) 1/2A2(g) +1/4B2(g) Kc` = (1/Kc)1/2 = (1/4)1/2 = = 0.53. Equilibrium Constant ExpressionExample 7At a certain temperature:(I)SO3(g) + NO(g) SO2(g) + NO2(g)Kc1 = 0.25(II) NO(g) + 1/2O2(g) NO2(g)Kc2 = 2

Find the value of Kc for the reaction below at the same temperature.

SO2(g) + 1/2O2(g) SO3(g)3. Equilibrium Constant ExpressionSolutionI reaction must be reversed.(I)SO2(g) + NO2(g) SO3(g) + NO(g) Kc1 = 1/0.25(II) NO(g) + 1/2O2(g) NO2(g)Kc2= 2

SO2(g) + 1/2O2(g) SO3(g)Kc = Kc1x Kc2 = 1/0.25x2 = 83. Equilibrium Constant ExpressionThe Reaction Quotient, QcQc helps us predict the direction in which a reaction mixturewill proceed to reach equilibrium. Kc is determined when thereaction is at equilibrium at constant temperature. Qc isdetermined when the reaction is at non equilibrium conditions.Qc = Kc, then the reaction is at equilibrium.Qc>Kc , then the reverse reaction takes place to establish equilibrium.Qc