1. The problem statement, all variables and given/known data The relative compositions of the pollutants NO and NO2 in air are governed by the reaction NO + 1/2 O2 ⇔NO2 For air containing 21-mol% O2 at 25C and 1.0133 bar, what is the concentration of NO in parts per million if the total concentration of both nitrogen oxides is 5 ppm? Note ppm is taken on a molar basis for gases. 2. Relevant equations 3. The attempt at a solution For this problem I am not sure how to go about it. I am not 100% sure if ppm means moles/total moles. Also, I am not able to find out the concentration of NO2 at equilibrium, which is why I haven't been able to get the concentration of NO.