1.6 - Equilibria

• What state do all reversible reactions reach?

  Dynamic equilibrium state
• What is the general reaction for the formation of ammonia?

  N2 + 3H2 ⇌ 2NH3
• What are the two features of dynamic equilibrium?

  1. Forward and backward reactions occur at equal rates.
  2. Concentrations of reactants and products remain constant.
• What does the term 'position of equilibrium' refer to?

  The composition of the equilibrium mixture
• What happens if the position of equilibrium favors the reactants?

  The equilibrium mixture contains mostly reactants
• What does Le Chatelier’s principle help determine?

  How external conditions affect equilibrium
• What does Le Chatelier’s principle state about external changes?

  Equilibrium shifts to oppose the change
• What happens to equilibrium if temperature is increased?

  It shifts in the endothermic direction
• What is the effect of increasing temperature on ammonia yield?

  It gives a lower yield of ammonia
• What happens if temperature is decreased in a reaction?

  Equilibrium shifts in the exothermic direction
• What is the trade-off with low temperatures in reactions?

  Higher yield but slower reaction rates
• What effect does increasing pressure have on equilibrium?

  It shifts towards the side with fewer moles of gas
• What is the effect of increasing pressure on methanol yield?

  It gives a higher yield of methanol
• What happens if pressure is decreased in a reaction?

  Equilibrium shifts towards the side with more moles of gas
• What is the effect of pressure if moles of gas are equal on both sides?

  No effect on the position of equilibrium
• What is the impact of increasing pressure on reaction rates?

  It may give a higher yield and faster rate
• What does a catalyst do to equilibrium?

  No effect on position, speeds up rate
• What are the key factors affecting industrial equilibrium processes?

  • Temperature
  • Pressure
  • Catalyst
  • Yield and rate trade-offs
• What is the Haber process used for?

  • Producing ammonia
  • Conditions: T=450°C, P=200-1000 atm, catalyst=iron
• What is the Contact process used for?

  • Producing sulfur trioxide
  • Conditions: T=450°C, P=1-2 atm, catalyst=V2O5
• What is the hydration of ethene used for?

  • Producing ethanol
  • Conditions: T=300°C, P=70 atm, catalyst=conc H3PO4
• What is the production of methanol from CO used for?

  • Producing methanol
  • Conditions: T=400°C, P=50 atm, catalyst=chromium and zinc oxides
• What does carbon neutral mean?

  No net annual carbon emissions
• What is the importance of recycling unreacted reactants?

  Improves overall yields of processes
• What is the equilibrium constant expression for a general reaction?

  Kc = [C]^p [D]^q / [A]^m [B]^n
• What is the unit of Kc for the reaction N2 + 3H2 ⇌ 2NH3?

  mol$^{-2}$ dm$^{6}$
• How do you calculate equilibrium moles from initial moles?

  Initial moles - moles reacted
• How do you calculate equilibrium concentrations?

  Concentration = moles / volume
• What is the Kc expression for the reaction H2 + Cl2 ⇌ 2HCl?

  Kc = [HCl]^2 / [H2][Cl2]
• What is the Kc expression for the reaction N2 + 3H2 ⇌ 2NH3?

  Kc = [NH3]^2 / [N2][H2]^3
• How do you calculate the equilibrium concentration of a reactant?

  Concentration = moles / volume
• What is the Kc expression for the reaction SO2 + ½ O2 ⇌ SO3?

  Kc = [SO3] / [SO2][O2]^{1/2}
• What is the Kc expression for the reaction 2H2 + O2 ⇌ 2H2O?

  Kc = [H2O]^2 / [H2]^2[O2]
• How is equilibrium concentration calculated?

  Concentration = moles / volume
• What is the formula for Kc?

  Kc = [HCl(g)]² / ([H2(g)][Cl2(g)])
• What does it mean if Kc has no unit?

  Equal numbers of reactants and products
• What happens to Kc if temperature changes?

  Kc changes with temperature
• How does pressure affect Kc?

  Kc remains constant with pressure changes
• What effect do catalysts have on Kc?

  Catalysts have no effect on Kc
• What happens to equilibrium position if temperature is increased in an exothermic reaction?

  Equilibrium shifts left, Kc decreases