Module 5.1.2- How far?

• Mole fraction


  the ratio of the number of moles of solute in solution to the total number of moles of solute and solvent

  
• Partial pressure equation


  mole fraction x total pressure
• Units of Kc


  substitute units into an expression for Kc

  cancel common units

  concentration units= mol dm^-3

  
• Homogenous equilibria


  an equilibrium system in which all reactants and products are in the same state e.g. Haber Process

  
• Heterogenous equilbiria


  an equilibrium system in which some species are in a different state
• What does Kc only include


  Species that are (g) or (aq)Remember when forming the Kc equation to not use any species that are (s) or (l)
• Kp


  equilibrium constant for gas-phase reactions based on partial pressures of reactants and productsonly for GASES
• Working out Kp


  1) work out mole fractions of all species

  2) work out partial pressure (mole fraction x total pressure)

  3) substitute in Kp expression (remember only gases!)Units are the ones used in the question

  
• Le Chatelier's Principle (revision)

  Increasing pressure = equilibrium position shifts towards the side with the fewest gaseous molecules

  If temperature increases = equilibrium position shifts towards the endothermic direction

  If concentrations of a species increases= equilibrium position shifts towards the direction which reduces the concentration
• When Kc > 1


  products are favoured
• When Kc < 1

  reactants are favored
• When Kc = 1

  equilibrium is in the middle
• Writing Frame- effect of Kp temperature

  Kp does change- it only changes with temperature

  Increase/decrease of partial pressure of X increases/decreases the numerator/denominator of the Kc expression(Refer to exo/endothermic reaction)

  So more X/Y is made to decrease/increase the numerator/denominator to increase/decrease the equilibrium Kp
• Writing Frame- effect of Kc/p with concentration etc.

  Kc/p doesn't change- it only changes with temperature

  Increase/decrease of [X]/p(X) increases/decreases the numerator/denominator of the Kc expression

  So more X/Y is made to decrease/increase the numerator/denominator to restore the equilibrium Kc
• Writing frame- effect of Kc/p with PRESSURE


  Kc/p doesn't change - it only changes with temp The concentration/partial pressure of all reactants and products increase/decrease

  However, the numerator/denominator increases/decreases more/less

  So more X/Y is made to decrease/increase the numerator/denominator to restore/increase/decrease the equilibrium Kc/p.
• How does catalyst affect equilibrium constants

  They are unaffected. Catalysts affect the rate of a chemical reaction but not the position of equilibrium. Catalysts speed up both the forward and reverse reactions in the equilibrium by the same factor. Equilibrium is reached quicker but the equilibrium position is not changed.