When the pressure is increased in a reaction, the equilibrium will shift towards the side of the reaction with fewer moles of gas/Equilibria/Chemical_Equilibria/Effect_of_Pressure_on_Gas-Phase_Equilibria). This is because pressure is inversely related to volume, and the effects of changes in pressure are opposite of the effects of changes in volume. However, if the reaction has the same number of moles of gas on both sides, then changing the pressure will not cause a significant effect on the position of the equilibrium. Therefore, the effect of increasing pressure on a reaction depends on the number of moles of gas on each side of the reaction.