How many ml of oxygen is required to fully combust propane to produce 785 ml of carbon dioxide?

Question

I really don't understand how to solve it, i only have the balanced chemical equation.

Answer 1

C₃H₈(g) + 5 O₂(g) --> 3 CO₂(g) + 4 H₂O(g)

To answer this question, we need to establish ratios we can use that allows us to convert between carbon dioxide and oxygen. If we assume this is at STP (standard conditions for temperature and pressure), we have our first ration one mole of an ideal gas is equal to 22.4 L. From the above equation, we have a second ratio where 5 moles of O₂ is needed to produce for every 3 moles of CO₂. Now we can use dimensional analysis to solve the problem. (Note: at STP, all volumes are in liters).

1.) Convert mL to L: 785 ml CO₂ = 0.785 L CO₂

2.) Use dimensional analysis to cancel out units, we use what we have to obtain what we want:

0.785 L CO₂ (1 mol CO₂/ 22.4 L CO₂) ( 5 mol O₂/ 3CO₂ mol) (22.4 L O₂/ 1 mol O₂) = 1.308 L O₂.

Therefore, 1308 mL of oxygen will be needed.