Calculate the volume of ethene reacted. Show your work.

Question

When ethene, C2H4 (g), is completely combusted, carbon dioxide, CO2(g), and water vapor, H2O(g), are produced according to the following balanced equation: 

C2H4 (g) + 3 O2 (g) → 2 CO2 (g) + 2 H2O (g)

If 11.2 L of carbon dioxide gas is produced at STP, answer questions a – c.

(Assume that all volume measurements are made at the same temperature and pressure) 

Answer 1

Hi Aisha,

What we're doing here is finding the amount of a reactant that is needed to produce a given amount of product. For this, all you need to do is find the molar ratio between the two compounds, given by the chemical equation. This chemical equation tells us that any time we put in one mole of C2H4, we make 2 moles of CO2. We know how much CO2 we have, so all we need to do is convert the unit that it's given to us in (L) into moles because our ratio is in moles. At STP, there is a simple conversion factor that 22.4L of a gas equals 1 mole. So since we have 11.2 L of gas, to find how many moles that is we divide by 22.4, giving us 0.5 mol CO2. Now that we know how many moles of CO2 were made, we can figure out how many C2H4 had to react. Every 2 moles of CO2 requires 1 mole of C2H4, so if we divide our moles of CO2 by 2, we will get the moles of C2H4. 0.5/2 is 0.25 mol C2H4. Now we know how much ethene was reacted, and all we have to do to get our final answer is a unit conversion from moles to volume. For this, we can use the same conversion factor as before: 22.4 L/mol. Since we want to go from mol to L, this time we multiply by 22.4. 0.25*22.4 = 5.6 L of C2H4.