Equilibrium

• What is the equilibrium constant?

  Kc

  
• What are the two types of equilibria?

  Homogeneous equilibria

  Heterogenous equilibria
• Homogeneous equilibria


  A homogeneous equilibrium contains equilibrium species that all have the same state (reactants AND products).

  -> For example, all the species are gases

  
• Heterogeneous equilibria


  A heterogeneous equilibrium contains equilibrium species that have different/a mixture of states

  
• ANY SPECIES THAT ARE SOLID OR LIQUID ARE?

  OMMITTED FROM THE Kc EXPRESSION !!

  ONLY GASES AND AQUEOUS SUBSTANCES ARE
• Mole fraction


  No units for mole fractions as it is a ratio

  
• The sum of mole fractions is

  1
• Partial pressure (p)
• Equation linking partial pressure and mole fraction

  Partial pressure of a gas = mole fraction of that gas x total pressure
• Kp


  Kp is calculated in the same way Kc is calculated, but using partial pressure

  -> The units of Kp are kPa/Pa/atm

  -> Like calculating for Kc, solids and liquids are not included

  -> Just like Kc, a large Kp indicates that the equilibrium favours products, whereas a small Kp means that the equilibrium favours the reactants

  -> Kp only includes gas because only gases have partial pressures (ignore any other species - (s)/(l)/(aq))
• What is the effect of temperature on equilibrium constant?

  If the forward reaction is exothermic:

  -> the equilibrium constant decreases (shifts to the left) with increasing temperature and raising the temperature decreases the equilibrium yield of products. The ratio __ is less than/greater than Kp/Kc

  If the forward reaction is endothermic:

  -> the equilibrium constant increases (shifts to the right) with increasing temperature and raising the temperature increases the equilibrium yield of products. The ratio is less than/greater than Kp/Kc
• What is the effect of concentration and pressure on equilibrium constants?

  The value of an equilibrium constant (K) is unaffected by the changes in concentration pressure - the equilibrium shift results from the very fact that the equilibrium constant does NOT change.

  For equilibrium constants and concentration changes:

  -> Ratio is less than/greater Kc and the system is no longer in equilibrium

  For equilibrium constants and pressure changes:

  -> Ratio is less than/ greater than Kp
• How do catalysts affect equilibrium constant

  Equilibrium constants are unaffected by the presence of a catalyst

  -> Catalysts affect the rate of a chemical reaction, but not the position. They speed up both the forward and reverse reactions in the equilbrium by the same factor