1. The problem statement, all variables and given/known data http://i.minus.com/jbzyIAyMvUrADW.png [Broken] 2. Relevant equations Conservation of mass in a closed system. 3. The attempt at a solution I'm not sure what the lecture is getting at here. Why is it that the number of moles of NO2 added to twice the number of moles of N2O4 = the total moles? Shouldn't it be the other way around?