[Thermodynamics] Density of Air
By: Tao Steven Zheng (鄭濤)
【Problem】
The composition of air is roughly 80% nitrogen and 20% and oxygen. Calculate the density of air under normal temperature and pressure conditions (NTP).
NTP is defined as the condition when temperature is 20 degrees Celsius and the pressure is 1 atmosphere.


【Solution】
Step 1: Calculate Mass
Nitrogen and oxygen gas are diatomic, so the molar mass is
To calculate the mass of 1 mole of air is
Thus 1 mole of air weighs 0.02880 kg.
Step 2: Calculate Volume
To calculate the volume of 1 mole of air at NTP
Step 3: Calculate Density
The density of air is simply the mass divided by the volume:
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