5.1.2 partial pressure and mole fractions

• How is mole fraction calculated?

  Mole fraction = moles of gas/total moles
• What is a common examiner trick used with mole fractions?

  Subtract the mole fractions from 1
• How is partial pressure calculated?

  Total pressure x mole fraction
• What is the sum of all partial pressures?

  Total pressure
• What extra labels are added to the equilibrium grid when using gas pressures?

  Mole fraction and partial pressure
• What units are used for pressure?

  KPa, Pa, atm and Bar
• What is Kp?

  Equilibrium constant applied to gases
• What does Kp tell us?

  The position of equilibrium
• What is the relationship between Kp and equilibrium amounts?

  The larger Kp, the more products
• How are substances represented in Kp expressions?

  p(substance) raised to the power of balancing number
• What mistake must you avoid when writing a Kp expression?

  Accidentally using square brackets instead of p(substance)
• In the Kp expression, where are products and reactants located?

  Products are the numerator, reactants are the denominator
• What happens to Kp or Kc when concentration or pressure are changed?

  Kp and Kc are constant
• What condition can alter Kp or Kc?

  Temperature
• How do you know how temperature affects Kp or Kc?

  By observing changes in equilibrium
• If a reaction is endothermic in the forwards direction, what happens to Kp when temperature is increased?

  Kp increases
• If the forwards reaction is exothermic and temperature is increased, what happens to Kp?

  Kp decreases
• If a reaction has more molecules of products than reactants, what happens to Kp when pressure is increased?

  Kp is constant
• If reactants have more moles than products, what happens to Kp when pressure is increased?

  Kp decreases
• If reactants and products have equal moles and pressure is changed, what happens to Kp?

  No change
• What are the effects of changing conditions for Kp?

  • Same effects as for Kc
  • Only temperature affects Kp value
  • Higher Kp favors products
• How is partial pressure defined in a mixture of gases?

  • Pressure exerted by one gas alone
  • p = (n/n₁) P
  • n = moles of gas, n₁ = total moles
• How are moles of each gas at equilibrium calculated?

  • Using the equilibrium grid
  • Initial, reacted, equilibrium values
  • Mole fraction and partial pressure