Change in Partial Pressure or Concentration

Consider the gasphase equilibrium,

If we add more CO and so increase PCO, Le Chatelier's principle states that the system will respond in such a way as to decrease PCO. It does this by reacting to consume CO, producing more CH₃OH (and incidentally consuming H₂). A similar argument applies to solution-phase equilibrium: increasing the concentration of one species will shift the equilibrium to consume that species.