5.2 Equilibria

• What are mole fractions and partial pressures used for?

  K calculations

  
• What is a mole fraction?

  Fraction of total moles for each chemical
• What does partial pressure represent?

  Pressure exerted by each gas in a mixture

  
• What symbol is used for partial pressure?


  p
• How is total pressure calculated?

  Sum of all partial pressures
• What is Dalton's Law?

  Total pressure equals sum of partial pressures
• What two pieces of information are needed to find partial pressure?

  Total pressure and mole fraction

  
• How do you calculate concentration?

  Concentration = number of moles / volume
• What calculations are expected in equilibrium calculations?

  • Calculating concentrations
  • Calculating mole fractions
  • Calculating partial pressures

  
• How do you calculate the concentration of ethanoic acid at equilibrium?

  [CH₃COOH] = 0.235 / 0.500 = 0.470 mol dm^-3
• What is the concentration of ethanol at equilibrium?

  [C₂H₅OH] = 0.035 / 0.500 = 0.070 mol dm^-3
• What is the concentration of ethyl ethanoate at equilibrium?

  [CH₃COOC₂H₅] = 0.182 / 0.500 = 0.364 mol dm^-3
• What is the concentration of water at equilibrium?

  [H₂O] = 0.182 / 0.500 = 0.364 mol dm^-3
• How do you determine equilibrium concentrations from initial concentrations?

  • Use initial, change, and equilibrium table
  • Apply molar ratios from stoichiometric equation

  
• What is the balanced equation for the hydrolysis of ethyl ethanoate?

  CH₃COOC₂H₅ (l) + H₂O (l) ⇌ CH₃COOH (l) + C₂H₅OH (l)
• How do you calculate the concentration of ethyl ethanoate at equilibrium in hydrolysis?

  [CH₃COOC₂H₅] = 0.0654 / 1.00 = 0.0654 mol dm^-3
• What is the concentration of water at equilibrium in hydrolysis?

  [H₂O] = 0.0654 / 1.00 = 0.0654 mol dm^-3
• What is the concentration of acetic acid at equilibrium in hydrolysis?

  [CH₃COOH] = 0.0346 / 1.00 = 0.0346 mol dm^-3
• What is the concentration of ethanol at equilibrium in hydrolysis?

  [C₂H₅OH] = 0.0346 / 1.00 = 0.0346 mol dm^-3
• What are the steps to calculate mole fractions and partial pressures?

  1. Calculate mole fractions of gases
  2. Use total pressure to find partial pressures

  
• How do you calculate mole fractions for nitrogen, hydrogen, and ammonia?

  Sum of moles divided by total moles

  
• What is the total pressure for the nitrogen and hydrogen reaction?

  150 kPa
• What is the partial pressure of nitrogen at equilibrium?

  29.25 kPa

  
• What is the partial pressure of hydrogen at equilibrium?

  87.75 kPa
• What is the partial pressure of ammonia at equilibrium?

  33.0 kPa
• What does K represent in equilibrium expressions?

  Equilibrium constant

  
• How is K calculated for a general reaction?

  K = [C]^c [D]^d / [A]^a [B]^b
• What is the significance of solids and liquids in K expressions?

  They are ignored in K expressions
• What happens to K if temperature changes?

  K changes only with temperature changes
• What does Le Chatelier's Principle state?

  Equilibrium shifts to counteract changes
• How does temperature affect exothermic reactions?

  Increasing temperature shifts equilibrium left

  
• How does temperature affect endothermic reactions?

  Increasing temperature shifts equilibrium right

  
• How does pressure affect gaseous equilibria?

  Pressure changes affect gaseous reactions
• What is the effect of a catalyst on K?

  Catalysts do not affect K
• What happens when a catalyst is added to a reaction?

  Reaction reaches equilibrium faster
• What factors affect the value of K?

  • Only temperature changes affect K
  • Other changes shift equilibrium position
  • Catalysts do not affect K