Explain the effect of increasing concentraion of O2 on the equilibrium position of this gas phase reaction and what you might see given that Nitrogen Oxide and Nitrogen Dioxide appear colourless and brown respectively. NO + 0.5O2 ----> NO2

Using "Le Chatelier's principle", the equilbrium will seek to oppose the change made to the reaction. In order to counter the increase in oxygen concentration, the reaction will shift to the right in order to decrease the new oxygen concentration. Given that NO is colourless, the reaction prior to the change would appear a pale brown, however upon the change in oxygen concentration, the concentration of NO₂will increase due to the forward reaction being now more thermodynamically favoured, so the reaction container would now appear a darker brown, as there is more (greatrer concentration/partial molar volume) of NO₂.