Question

Assuming that the volumes of carbon diox-
ide and of propane are measured under the
same experimental conditions, what volume
of carbon dioxide is produced by the complete
combustion of 20 L of propane?


i just don't understand

Answer 1

This is just another stoichiometry problem but since everything is a gas and measured at the same conditions, it allows us to use a shortcut.

C3H8 + 5O2 ==> 3CO2 + 4H2O

We may use volume in liters as if L = mols. Simply convert L C3H8 to L CO2 using the coefficients in the balanced equation.
20 L C3H8 x (3 mol CO2/1 mol C3H8)= 20 x (3/1) = 60 L CO2.