Please Help?

Liters of CO2 at STP.....

Simply use the unit-factor method where you have a one-line setup, one chain calculation, no intermediate answer to deal with and almost zero chance of error. There are two conversion factors. One comes from the balanced chemical equation, and the other from the definition of a mole.

Use these equivalences to make a conversion factor, or mix and match to make more.
1 mol = 1 molar mass
1 mol = 6.022x10^23 particles
1 mol = 22.414 L of any ideal gas at STP

2C2H2(g) + 5O2(g) --> 4CO2(g) + 2H2O(g)
18.4 mol .........................?L

18.4 mol C2H2 x (2 mol CO2 / 1 mol C2H2) x (22.414L CO2 / 1 mol CO2) = 825 L CO2

Check the units: mol C2H2 cancels out, and mol CO2 cancel out, leaving L of CO2. Since you a looking for a volume of CO2, you know the setup is correct and that you will get the right answer.

The correct balanced equation should be :
2C₂H₂ + 5O2 → 4CO₂ + 2H₂O
Mole ratio C₂H₂ : CO₂ = 2 : 4 = 1 : 2

No. of moles of C₂H₂ burned = 18.4 mol
No. of moles of CO₂ formed (but not used) = (18.4 mol) × 2 = 36.8 mol

Each mole of CO₂ occupies a volume of 22.4 L at STP.
Volume of CO₂ formed at STP = (46.8 mol) × (22.4 L/mol) = 824 L (to 3 sig. fig.)

The answer: 824 L

nerd