Final answer:
Removal of O₂ (g) from a reaction at equilibrium will cause the equilibrium to shift towards the reactant side to increase its concentration and re-establish equilibrium, decreasing the concentration of products like NO.
Step-by-step explanation:
When O₂ (g) is removed from the reaction at equilibrium, Le Chatelier's Principle predicts that the equilibrium will shift towards the side where O₂ is a reactant to increase its concentration and re-establish equilibrium. For the reaction N₂(g) + O₂(g) = 2NO(g), this means the concentration of N₂ and NO will decrease, and the concentration of O₂ will attempt to increase. Removal of a reactant causes the equilibrium to shift left, favoring the formation of reactants.
If O₂ is added, the equilibrium shifts to the right, increasing the concentration of NO while the concentrations of N₂ and O₂ will decrease as more gets converted to NO. If N₂ is removed, the equilibrium shifts to the left, reducing the concentration of NO and attempting to increase the concentration of N₂. Adding NO will shift the equilibrium to the left, thus increasing the concentrations of N₂ and O₂ while decreasing the concentration of NO. Decreasing the volume of the reaction vessel favors the side with fewer moles of gas, and since there are 3 moles of gas on the reactant side and 2 moles on the product side for this reaction, decreasing volume would shift the equilibrium to the right, increasing NO concentration.