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

I know that #"C"_3"H"_8+5"O"_2rarr3"CO"_2+4"H"_2"O"# and I got #0.2"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?

1 Answer
Doc048
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^oC# & 1Atm Pressure. The tables, however, specify standard thermodynamic values which are at #25^oC#. This is an issue if calculating volume values as 1 mole of gas at #0^oC# is 22.4L/mole but slightly larger at #25^oC# 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_oC# = mass at #25^oC#.

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

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