1.10 Kp for homogeneous systems

homogeneous equilibrium = reactants and products are in the same phase/state

heterogeneous equilibrium = reactants and products are in different phases/states


Kp is the equilibrium constant for a reversible reaction occuring in the gas phase at a constant temperature

  • gaseous homoegeneous equilibrium

  • Kp is greater than 1 = equilibrium lies towards the products

  • Kp is equal to 1 = equilibrium lies in the centre

  • Kp is less than 1 = equilibrium lies towards the reactants


Kp is only affected by changes in temperature

  • the equilibrium position change due to temperature change leads to different concentrations of reactants and products

  • changes in pressure shift the position of equilibrium to a new position that restores Kp so same Kp value

  • use of catalyst only causes reaction to reach equilibrium faster, but does not change value of Kp

the exact same reaction can have a different Kp value if a different temperature is used


(pp A) = partial pressure of A in kPa, must not use square brackets

ICE table to find equilibrium moles

mole fraction of A

= (equilibrium moles of A) / (total equilibrium moles in the system)

partial pressure of A in mixture

= (mole fraction of A) x (total pressure of the system)

all reactants and products in the gas phase