# How many moles of propane gas ("C"_3"H"_8) can be burned with 1 mole of oxygen gas at STP?

## I know that $\text{C"_3"H"_8+5"O"_2rarr3"CO"_2+4"H"_2"O}$ and I got $0.2 \text{mol}$, but that seems too easy for the worksheet it was on. Is the fact that it's at STP just extra info to throw me off or am I missing something?

Apr 26, 2017

You are correct. 1 mole ${O}_{2}$ consumes 1/5th mole (0.20 mole) propane.

#### Explanation:

The equation as written is 'assumed' to be at STP if written using 'Standard State' formulas published in Thermodynamics Properties Tables. Of course STP represents (in most college texts) ${0}^{o} C$ & 1Atm Pressure. The tables, however, specify standard thermodynamic values which are at ${25}^{o} C$. This is an issue if calculating volume values as 1 mole of gas at ${0}^{o} C$ is 22.4L/mole but slightly larger at ${25}^{o} C$ at 24.45L/mole.

${V}_{25}$ = (298/273)(22.4 L/mole) = 24.45 L/mole

For 'mass' calculations, it does not matter. mass at ${0}_{o} C$ = mass at ${25}^{o} C$.

Your use of the equation reaction ratios in the balanced equation are spot on correct.