Equilibrium Constant Kp

• Partial pressure


  The pressure that a gas would have if it alone occupied the volume occupied by the whole mixture
• If a mixture of gases contains 3 different gases then the total pressure will equal the 3 partial pressures added together
• Partial pressure of a gas

  Mole fraction of the gas x total pressure
• Calculating mole fraction


  Number of moles of a gas / total number of moles of all gases
• Kp


  Equilibrium constant based on partial pressures of gases
• Only include gases in the Kp expression. Ignore solids, liquids, and aqueous substances.
• The unit of Kp is kPa^-2
• Kc and Kp only change with temperature. They do not change if pressure or concentration are altered. A catalyst also has no effect on Kc or Kp.
• If temperature is increased

  The reaction shifts to oppose the change and move in the backwards endothermic direction. The position of equilibrium shifts left. The value of Kp gets smaller.
• If pressure is increased

  The reaction shifts to oppose the change and move in the forward direction to the side with fewer moles of gas. The position of equilibrium shifts right. The value of Kp stays the same.