Gases Part 2. Standard Temp and Pressure, STP. For gases, chemists have defined a standard set of conditions: standard temperature and pressure or STP. STP is defined as 1.00 atm pressure and 0°C or 273.15K.
n = g/MW where MW is the molar mass (really mol. mass)
1) Gases have negligible volume!
2) Gas particles have no interactions!