re: propane concentration

[SLW]

I'm trying to determine the concentration of CO2 in a house produced by a space heater. The space heater produced 330 kW and ran for 2 hours. I can calculate the number of moles of CO2 (54, I think), but don't know how to get it into a concentration.

[Guest]

I'm trying to determine the concentration of CO2 in a house produced by a space heater. The space heater produced 330 kW and ran for 2 hours. I can calculate the number of moles of CO2 (54, I think), but don't know how to get it into a concentration.

I think you are a bit off, and I think your real concern should be carbon monoxide, not carbon dioxide. Humans can tolerate up to 4% carbon dioxide, but only 120 ppm 0.00012% carbon monoxide. Since CO represents incomplete or imperfect combustion, there is no good way to estimate it through stoichiometric analysis.

As for total carbon: http://hypertextbook.com/facts/2002/EricLeung.shtml
Energy content of propane is 12.9 kWh/kg, so I calculated the above is about 51 kg of C3H8. Since it is 36/44 carbon, that is about 42 kg of carbon, or 3490 mol at 12 g/mol. That carbon will be in an unpredictable mix of CO2 (hopefully all), CO and HC (unburnt hydrocarbons), the last two being very bad for you.

As for concentration, you'd have to compare that to the total volume of air in the house, including what leaks in (or out, but don't double count) in two hours. The leakage over two hours is mostly likely larger than the volume of the house, but that would depend on windows, weatherstripping, etc.

If I ignore air leakage, a 2000 sq ft house with normal ceilings would have very roughly 200 m^2 of floor, 400 m^3 of air volume. At 20 degrees C, that is about 33000 moles of air. If 10% of that is CO and CO2, I assume you are investigating a fatality. If not, the house leaks like a sieve, or someone is very likely (or I overlooked a major error, somewhere).

If you are investigating a fatality, please note I have rounded liberally, and the numbers are only good to 1-2 figures and should be redone precisely.

[Guest]

Sorry, that is about 17000 moles of air in the house. I must have hit a wrong key.