Consider the following chemical equation : 2NO2(g)=N2O4(g). If 25.0mL of NO2 gas is completely converted to N2O4 gas under the same conditions, what volume will the N2O4 occupy?

Answer 1

25.0 mL NO2 x (1 mol N2O4/2 mols NO2) = 25.0 x 1/2 = ?
This is a short cut in which volume is used as if it were mols. You can do that since the conditions are the same .