The decomposition of NO2 to NO and O2 : 2NO2(g) 2NO(g) + O2(g) has been experimentally determined to be second order with respect to the NO2 concentration. A reaction begins at time = 0 with an unknown initial concentration of pure NO2(g). After 2h, the rate of O2 gas production is measured as 1.010^-10 mol/(cm3s). If the reaction rate constant for this reaction is k = 10 (mol/cm3s)^-1, determine what the initial concentration of NO2(g) must have been when the reaction began.