And the reason we're using partial pressures is because every single reactant is in the gas state. Let me just add the G and G for gas. So our equilibrium or partial pressure equilibrium constant given by KP equals the partial pressure of our product to the second power because we have a two coefficient divided by the partial pressure due to this gas molecule times the partial pressure due to this gas molecule to the third power. The third comes from the coefficient and the one here comes from the one coefficient. Notice that our gas molecule, this one does not appear in our equilibrium expression and that means adding this guide will have no effect on our chemical equilibrium and in fact, adding any other molecule, for example helium to our mixture will not do anything to our chemical equilibrium. And that's an important point to understand only increasing the concentrations of molecules that are actually present in our reaction in our equilibrium expression will affect our chemical equilibrium.