IB Chemistry on Le Chatelier's Principle, Equilibrium Constant and Dynamic Equilibrium
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IB Chemistry on Le Chatelier's Principle, Equilibrium Constant, Kc and Dynamic Equilibrium

IB Chemistry on Le Chatelier's Principle, Equilibrium Constant, Kc and Dynamic Equilibrium

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IB Chemistry on Le Chatelier's Principle, Equilibrium Constant and Dynamic Equilibrium Presentation Transcript

  • 1. Factors affecting the position of Equilibrium Le Chatelier’s Principle• A system in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again Effect of Concentration on the position of equilibrium • Increase in Conc ↑ - position of equilibrium shift to right/left - Conc will be Reduced ↓ • Decrease in Conc ↓ – position of equilibrium shift to right/left - Conc will be Increased ↑ Fe3+ + SCN- ↔ Fe(SCN)+2 (yellow) (red Blood) Click to view videoIncrease SCN- or Fe3+ Conc Decrease Fe3+ Conc•Equilibrium shift to right → • By adding OH- will shift equilibrium to left ←•Formation of complex ion Fe(SCN)2+ (red blood) •Fe(SCN)2+ breakdown to form more Fe3+ (yellow) Decrease SCN- Conc • By adding Ag+ will shift equilibrium to left • Fe(SCN)2+ breakdown to form more SCN- (yellow) Increase Concentration • Rate of reaction increase ↑ • Rate constant - no change • Kc, equilibrium constant - no changes • Position of equilibrium shifted to a side to decrease concentration again ↓
  • 2. Factors affecting the position of Equilibrium Le Chatelier’s Principle• A system in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again Effect of Concentration on the position of equilibrium • Increase in Conc ↑ - position of equilibrium shift to right/left - Conc will be Reduced ↓ • Decrease in Conc ↓ – position of equilibrium shift to right/left - Conc will be Increased ↑ 2CrO42- + 2H+ ↔ Cr2O72- + H2O (yellow) (orange) Click to view video Decrease H+ Conc Increase H+ Conc • By adding OH- • By adding H+ •Equilibrium shift to left ← • Shift equilibrium to right → •Formation of CrO42- (yellow) • Formation of Cr2O72- (orange) Increase Concentration • Rate of reaction increase ↑ • Rate constant - no change • Kc, equilibrium constant - no changes • Position of equilibrium shifted to a side to decrease concentration again ↓
  • 3. Factors affecting the position of Equilibrium Le Chatelier’s Principle• A system in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again Effect of Concentration on the position of equilibrium • Increase in Conc ↑ - position of equilibrium shift to right/left - Conc will be Reduced ↓ • Decrease in Conc ↓ – position of equilibrium shift to right/left - Conc will be Increased ↑ CoCl42- + 6H2O ↔ Co(H2O)62+ + 4CI – (blue) (pink) Click to view video Decrease CI- Conc Increase H2O Conc Increase CI- Conc •By adding Ag+ to form AgCI • By adding H2O • By adding HCI •Equilibrium shift to right → • Shift equilibrium to right → • Shift equilibrium to left ← •Formation of Co(H2O)62+ (pink) • Formation of Co(H2O)62+ (pink) • Formation of CoCl42- (blue) Increase Concentration • Rate of reaction increase ↑ • Rate constant - no change • Kc, equilibrium constant - no changes • Position of equilibrium shifted to a side to decrease concentration again ↓
  • 4. Factors affecting the position of Equilibrium Le Chatelier’s Principle• A system in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again Effect of Pressure on the position of equilibrium Increase in pressure ↑ - favour reaction with a decrease in pressure ↓ Decrease in pressure ↓ - favour reaction with an increase in pressure ↑ N2O4 (g) ↔ 2NO2(g) (colourless) (brown) Click to view video Increasing Pressure ↑ Decreasing Pressure ↓ • By reducing Volume • By Increasing Volume • Equilibrium shift to left ← • Equilibrium shift to right → • Less molecules on left side • More molecules on right side •Pressure drops ↓ •Pressure increase ↑ • Formation of N2O4 (colourless) • Formation of NO2 (brown) Increase Pressure • Rate of reaction increases • Rate constant unchanged • Position of equilibrium shift to reduce pressure • Kc, equilibrium constant unchangedIncrease pressure ↑ – collision more frequent - shift equilibrium to left - to reduce number of molecules - pressure decrease again ↓Decrease pressure ↓ – collision less frequent – shift equilibrium to right – to increase number of molecules – pressure increase again ↑
  • 5. Factors affecting the position of Equilibrium Effect of Pressure on the position of equilibriumIncrease in pressure ↑ - favour reaction with a decrease in pressure ↓Decrease in pressure ↓ - favour reaction with an increase in pressure ↑ N2O4 (g) ↔ 2NO2(g) (colourless) (brown) Click to view videoIncreasing Pressure ↑ Decreasing Pressure ↓• By reducing Volume • By Increasing Volume• Equilibrium shift to left ← • Equilibrium shift to right →• Less molecules on left side • More molecules on right side•Pressure drops ↓ •Pressure increase ↑• Formation of N2O4 (colourless) • Formation of NO2 (brown) N2(g) + 3H2(g) ↔ 2NH3(g) ( 4 vol/moles ) (2 vol/moles) Increasing Pressure ↑ Decreasing Pressure ↓ • Equilibrium shift to right → • Equilibrium shift to left ← • Less molecules on left side • More molecules on right side •Pressure drops ↓ •Pressure increase ↑ • Formation of NH3 (product) • Formation of H2 and N2 (reactants)
  • 6. Factors affecting the position of Equilibrium Le Chatelier’s Principle• A system in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again Effect of Temperature on the position of equilibrium Increase in Temp ↑ – Favours endothermic reaction – Absorb heat to reduce Temp again ↓ Decrease in Temp ↓ – Favours exothermic reaction – Release heat to increase Temp again ↑ CoCl42- + 6H2O ↔ Co(H2O)62+ + 4CI – ΔH = -ve (exothermic) (blue) (pink) Click to view video Increase Temp ↑ Decrease Temp ↓ • By Heating it up • By Cooling it down • Favours endothermic reaction • Favours exothermic reaction • Equilibrium shift to left ← • Equilibrium shift to right → • To reduce Temp • To increase Temp • Formation of CoCl42- (blue) • Formation of Co(H2O)62+ (pink) Increase Temperature • Rate of reaction increases • Rate constant also changes • Rate of forward and Rate of reverse increases but to different extend • Position of equilibrium shift to endothermic to decrease Temp • Kc, equilibrium constant change
  • 7. Factors affecting the position of Equilibrium Le Chatelier’s Principle• A system in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again Effect of Temperature on the position of equilibrium Increase in Temp ↑ – Favours endothermic reaction – to absorb heat to reduce Temp again ↓ Decrease in Temp ↓ – Favours exothermic reaction – to release heat to increase Temp again ↑ N2O4 (g) ↔ 2NO2(g) ΔH = + 54kJmol-1 (colourless) (brown) Click to view video Increase Temp ↑ Decrease Temp ↓ • By Heating it up ↑ • By Cooling it down ↓ • Favours endothermic reaction • Favours exothermic reaction • Equilibrium shift to right → • Equilibrium shift to left ← • To reduce Temp ↓ • To increase Temp ↑ • Formation of NO2 (brown) • Formation of N2O4 (colourless) Increase Temperature • Rate of reaction increases • Rate constant also changes • Rate of forward and Rate of reverse increases but to different extend • Position of equilibrium shift to endothermic to decrease Temp • Kc, equilibrium constant change
  • 8. Factors affecting the position of Equilibrium Effect of Temperature on equilibrium constant, Kc Rate forward = kf A ↔ Rate reverse = kr B ΔH = +veArrhenius Equation show the relationship between temperature and rate constant• Temperature will affect the rate constant for forward and reverseIncrease Temp ↑ – equilibrium shift to right, endothermic side to decrease Temp ↓ - more product B producedRate of forward kf > Rate of reverse krKc = kf/kr or [conc product]/[conc reactant]Kc increase ↑ because ratio of kf/kr increase ↑ or ratio of product /reactant increase ↑DecreaseTemp ↓ – equilibrium shift to left - exothermic side to increase Temp - more reactant A producedRate of reverse kr > kfKc = kf/krKc decrease ↓ because ratio of kf/kr decrease ↓ or ratio of product /reactant decrease ↓ N2O4 (g) ↔ 2NO2(g) ΔH = + 54kJmol-1 For endothermic reaction Increase Temp ↑- position equilibrium shift to right – endothermic side – to absorb heat – Temp decrease ↓ Increase Temp ↑ – forward rate, kf > reverse rate, kr - Kc = kf/kr = Kc increase ↑ Increase Temp ↑- more product form, less reactants – Kc = ratio of product/reactants – Kc increases ↑ Conclusion : Endothermic Reaction – Temp increase ↑ – Kc increase ↑ – Product increase ↑
  • 9. Factors affecting the position of Equilibrium Effect of Temperature on equilibrium constant, Kc Rate forward = kf A ↔ Rate reverse = kr B ΔH = -veArrhenius Equation show the relationship between temperature and rate constant• Temperature will affect the rate constant for forward and reverseIncrease Temp ↑ – equilibrium shift to left, endothermic side to decrease Temp ↓ - more reactant A producedRate of reverse kr > Rate of forward kfKc = kf/kr or [conc product]/[conc reactant]Kc decrease ↓ because ratio of kf/kr decrease ↓ or ratio of product /reactant decrease ↓DecreaseTemp ↓– equilibrium shift to right - exothermic side to increase Temp ↑ - more products B producedRate of forward kf > krKc = kf/krKc increase ↑ because ratio of kf/kr increase ↑ or ratio of product /reactant increase ↑ H2(g) + I2(g) ↔ 2HI(g) ΔH = -9.6kJmol-1 For exothermic reaction Increase Temp ↑- position equilibrium shift to left – endothermic side – to absorb heat – Temp decrease ↓ Increase Temp ↑ – reverse rate, kr > forward rate, kf - Kc = kf/kr = Kc decrease ↓ Increase Temp ↑- more reactant form, less product – Kc = ratio of product/reactants – Kc decreases ↓ Conclusion : Exothermic Reaction – Temp increase ↑ – Kc decrease ↓ – Product decrease ↓
  • 10. Factors affecting the position of Equilibrium Effect of Catalyst on equilibrium constant, Kc Catalyst • Provide an alternative pathway with lower activation energy • Increase the rate of forward and reverse to the same extent/factor • Position of equilibrium and Kc remains unchange • Catalyst shorten the time it takes to reach equilibriumWithout catalyst, takes long reaching equilibrium With catalyst, reaching equilibrium fast N2(g) + 3H2(g) ↔ 2NH3(g) ΔH = - 92kJmol-1Effect of catalyst on Rate, Rate constant and Kc on ammonia productionAdding catalyst• Rate increase ↑• Rate constant increase ↑• Equilibrium constant Kc – No change• Amount of product and reactants remain the unchanged
  • 11. Equilibrium LawWhen a reversible reaction achieved dynamic equilibrium - aA + bB ↔ cC and dD• Equilibrium constant Kc = ratio of molar conc of product (raised to power of their respective stoichiometry coefficient) tomolar conc of reactants (raised to power of their respective stoichiometry coefficient)• Kc is constant at constant temperature aA + bB ↔ cC and dD Kc = (C)c(D)d (A)a(B)bAt equilibrium: N2O4 (g) ↔ 2NO2 (g) N2O4 (g) ↔ 2NO2 (g) Rf (rate forward) = Rr (rate reverse) Kc = kf / kr Rf (rate forward) = Rr (rate reverse) kf [N2O4] = kr [NO2]2 kf [N2O4] = kr [NO2]2 Kc = (NO2)2 kf/kr = (NO2)2 (N2O4) (N2O4)• Kc is a ratio of rate constant and is temperature dependent• Kc is a ratio of products conc to reactants conc• Magnitude of Kc indicate how far/extend of the reaction proceeds towards a product at a given temperatureSmall Kc : N2(g) + O2(g) ↔ 2NO(g) Kc = 1 x 10 -30 small ↓ Kc = (NO)2 (N2)1(O2)1 Kc small → low product ↓, more reactants ↑, close to no reaction at allLarge Kc : 2COg) + O2 ↔ 2CO2(g) Kc = 2.2 x 10 22 high ↑ Kc = (CO2)2 (CO)2(O2)1 Kc large → high product ↑, small reactants ↓ , close to completionIntermediate Kc : 2HI(g) ↔H2(g) + I2(g) Kc = 0.02 Kc = (H2)(I2) (HI)2 Kc intermediate → significant amount of reactants and products
  • 12. Equilibrium Law Effect of Concentration on equilibrium constant, Kc • Increase in Conc ↑ - position of equilibrium shift to right/left - Conc will be Reduced ↓ • Decrease in Conc ↓ – position of equilibrium shift to right/left - Conc will be Increased ↑ Equilibrium Law applies to system at equilibrium • Kc is constant at constant temperature • Kc unaffected by Concentration, Pressure and Catalyst • Addition of reactants and products will only shift position of equilibrium to right or left changing to a new equilibrium concentration but Kc remains the same • Magnitude of Kc indicate the extend or how far the reaction forms product/reactants but not how fast • Kc High – High product but rate can be very slow • Kc Low – Low product but rate can be very fast Reaction between H2 + I2 ↔ 2HI Kc = 46.4 at 730K Kc = [HI]2 = 46.4 [H2][I2] Initial Conc H2 + I2 ↔ 2HI Equilibrium ConcReaction contain different Initial Conc of H2 and I2 and HI but at equilibium Kc remains the same regardless of initial conc Kc = [HI]2 = 46.4 [H2][I2] Kc unchanged
  • 13. How dynamic equilibrium is shifted when H2 is added ? N2(g) + 3H2(g) ↔ 2NH3 (g) • When more H2 added, position equilibrium will shift to right, to reduce the H2 conc and increase the NH3 conc • Rate of forward and reverse will increase • New equilibrium concentration will be achieved when rate of forward kf = rate of reverse kr • More products NH3 and less reactants N2 but Kc value remains unchanged H2 added New equilibrium ConcAt equilibrium Equilibrium shifted to right At equilibrium againRate forward kf = Rate reverse kr Rate forward kf > Rate reverse kr Rate forward kf = Rate reverse kr Kc = 4.07 Qc = 2.24 Kc = 4.07
  • 14. How dynamic equilibrium is shifted when H2 is added ? N2(g) + 3H2(g) ↔ 2NH3 (g) • When more H2 added, position equilibrium will shift to right, to reduce the H2 conc and increase the NH3 conc • Rate of forward and reverse will increase • New equilibrium concentration will be achieved when rate of forward kf = rate of reverse kr • More products NH3 and less reactants N2 but Kc value remains unchanged H2 added New equilibrium ConcEquilibrium Conc for H2 = 0.82M New Conc for H2 = 1.00M New Equilibrium Conc for H2 = 0.90MEquilibrium Conc for N2 = 0.20M Equilibrium Conc for N2 = 0.20M New Equilibrium Conc for N2 = 0.19MEquilibrium Conc for NH3 = 0.67M Equilibrium Conc for NH3 = 0.67M New Equilibrium Conc for NH3 = 0.75M N2(g) + 3H2(g) ↔ 2NH3 (g) N2(g) + 3H2(g) ↔ 2NH3 (g) N2(g) + 3H2(g) ↔ 2NH3 (g) • Kc = (NH3)2 • Qc = (NH3)2 • Kc = (NH3)2 (N2)(H2)3 (N2)(H2)3 (N2)(H2)3 • Kc = (0.67)2 • Qc = (0.67)2 • Kc = (0.75)2 (0.20)(0.82)3 (0.20)(1.00)3 (0.19)(0.90)3 • Kc = 4.07 • Qc = 2.24 Qc < Kc • Kc = 4.07 2.24 < 4.07 • Kc must remain constant • Shift to the right • Increase products and decrease reactants • New equilibrium Conc is achieved • Qc = Kc again