At NTP, what is the mass of "22.4 L" of nitrogen gas?

1 Answer
Aug 11, 2017

Well, I can set things up for you to calculate the mass... but weight is in newtons, "N", or "kg"cdot"m/s"^2... and you have to decide what the chemical formula of nitrogen is... you have a 50% chance of guessing it right!


Normal Temperature and Pressure, NTP, is apparently 20^@ "C" and "1 atm". This should not be confused with STP, which is at 0^@ "C", not 20^@ "C", and not 25^@ "C".

The "mass" version of the ideal gas law can be derived.

PV = nRT

n = (PV)/(RT)

To get the units from "mols" to "g", simply multiply by the molar mass M in "g/mol".

nM -= m = (PVM)/(RT)

In this case, we have:

  • P, pressure, in "atm", of the ideal gas within the container.
  • V, volume, in "L", of the ideal gas.
  • M, molar mass, in "g/mol", of the ideal gas.
  • R = "0.082057 L"cdot"atm/mol"cdot"K", the universal gas constant.
  • T, temperature, in "K", within the container filled with ideal gas.

In case you couldn't tell, we're assuming ideal gases... So, the mass is:

color(red)(m) = (cancel"1 atm" cdot 22.4 cancel"L" cdot M" g/"cancel"mol")/(0.082057 cancel"L"cdotcancel"atm""/"cancel"mol"cdotcancel"K" cdot (20 + 273.15 cancel"K"))

= color(red)(???)

Now, it's up to you to decide what the molar mass is.

What is the molar mass of "nitrogen"? Is it "14.007 g/mol", or "28.014 g/mol"? Why would you have to choose? (It matters!)