Effect of Pressure on Equilibrium

For gaseous reactions, if you change PRESSURE, the direction that the equilibrium shifts depends on the NUMBER OF MOLECULES (moles) on either side of the equation. These are the THREE scenarios you can have:

The more MOLECULES you have in a closed system, the GREATER the PRESSURE.

This means if you INCREASE the pressure of a system at equilibrium, it will try to COUNTERACT the change by DECREASING the pressure, so it will shift to the side with FEWER MOLECULES. The opposite will happen if you DECREASE the pressure.

This shifting of equilibrium can affect the amount of reactants and products in the system.

For an example where there are MORE MOLES on the LEFT:

If there are MORE MOLES on the RIGHT, the opposite would happen:

 If there are the SAME number of moles on the left and right, NOTHING HAPPENS.