1 gram of C3H8 gas and 1 gram of O2 gas are delivered to a metal sphere with a fixed volume of 1 L. After the two gases are introduced, the two reactants are ignited and burned according to the balanced reaction

Question

C3H8(g)+5O2(g)changes to3CO2(g)+4H2O(g)
After reaction, the sphere is held at 226.25 oC. What is the final pressure in the sphere given that all the compounds inside are gases and the limiting reagent is completely consumed with 100% yield ?

Answer 1

First determine which is the limiting reagent.
moles C3H8 = 1g/molar mass = about 0.02 but you need to do it more accurately.
moles O2 = 1g/molar mass = about 0.02.

Now convert moles C3H8 to moles CO2. I have about 0.06.
Convert moles O2 to moles CO2. I have about 0.02.
Both answers can't be correct; the correct value in limiting reagent problems is ALWAYS the smaller value and the reagent providing that value is the limiting reagent. Therefore, O2 is the limiting reagent.
Since all of that will be consumed, you should convert moles O2 to moles C3H8 to determine moles C3H8 consumed, then subtract from initial moles to determine how much C3H8 remains unreacted. Add moles C3H8 + moles CO2 + moles H2O and use PV = nRT to solve for final P.