calculating amount of air in room .. please help??

Question

i have a room of the volume of 2156 cubic feet. i need to calculate the amount of air in pounds of mass that is in the room.. how di i do that ??? i also need to find out the amount of water vapor that is in the room if the temp. is 70 deg fer. .. please help !!

Answer 1

To calculate this, you need to know your elevation above sea level, air pressure, and relative humidity. (you can find this data easily at www.wunderground.com)

You've already provided:
Volume = 2156 ft^3 = 60.4 m^3
Temperature = 70F = 294 K

And for the following example, I will assume:
Pressure (msl) = 1013 hPa (millibars)
Elevation = 300 meters
Humidity = 60%

Step 1: Compute your local station pressure from the MSL pressure given in the weather report.

Pstation = Pmsl * ((288 - 0.0065 Z) / 288) ^ 5.256
Pstation = 1013 * ((288 - 0.0065 *300) / 288) ^ 5.256
Pstation = 977 hPa

Step 2: Compute the saturation vapor pressure (i.e the partial pressure of water vapor, if the humidity were 100%)

Pvsat = 6.108 * 10 ^ ((7.5 T - 2048) / (T - 35.85))
Pvsat = 6.108 * 10 ^ ((7.5*294 - 2048) / (294 - 35.85))
Pvsat = 25 hPa

Step 3: Compute the actual vapor pressure (i.e the actual partial pressure of water vapor in your room)

Pv = Pvsat * RH
Pv = 25 hPa * .60
Pv = 15 hPa

Step 4: Compute the density of dry air in your room.

Dd = Pd / Rd * T
Dd = ((Pstation - Pv)*100) / (287 * 294)
Dd = ((977 - 15)*100) / (287 * 294)
Dd = 1.14 kg / m^3

Step 5: Compute the density of water vapor in your room.

Dv = Pv / Rv * T
Dv = (15 *100) / (461 * 294)
Dv = 0.011 kg / m^3

Step 6: Compute masses of dry air and water vapor.

Md = Dd * V
Md = 1.14 * 60.4
Md = 68.5 kg = 151 pounds

Mv = Dv * V
Mv = 0.011 * 60.4
Mv = 0.66 kg = 1.5 pounds

Thus, with the assumptions made, your room would contain approximately 152.5 pounds of ambient air: 151 pounds of dry air plus 1.5 pounds of water vapor.

Answer 2

Air at 70 degree F weighs 0.007492 pounds per cubic foot.

0.007492 x 3156 = answer


The amount of water vapor depends on the humidity.

Answer 3

Dry Air at 70 degrees F and at sea level weighs 0.075 pounds per cubic foot (= 13.349 cubic feet per pound) as taken from a table of "Thermodynamic Properties of Air".

So, the air in your room would weigh 161.7 pounds.

Answer 4

Try this. Convert the volume to cubic meters. Now air is 28g per mole and a mole is very close to 24.4L per mole at that temperature and there are 1000L in a cubic meter. You can do the arithmetic yourself.

Answer 5

my god that sounds difficult. Good luck