If 5.0 liters of carbon dioxide gas are produced by the reaction below at 273 K and 1.00 atm, how many liters of oxygen gas were used in the reaction?
2 CO (g) + O2 (g) yields 2 CO2 (g)

Question

If 5.0 liters of carbon dioxide gas are produced by the reaction below at 273 K and 1.00 atm, how many liters of oxygen gas were used in the reaction? 
2 CO (g) + O2 (g) yields 2 CO2 (g)

anonymous · Answer

10.0 L
 7.5 L
 5.0 L
 2.5 L

cuanchi · Answer

You have to look at the stoichiometry of the reaction.
The reaction is telling you that 
1 mole of O2 will produce 2 moles of CO2
Since the volume of a gas is independent of the kind of gas that you have and only dependent of the number of moles. This means that if you have one liter of a gas, it will have the same amount of moles that one liter of any other gas at the same temperature and pressure.
You can said that 1L O2 will produce 2L of CO2, you can made a conversion factor with this values and calculate the volume of O2
Then 
 
5L CO2 x 1L O2 / 2L CO2 = ????? L O2