1. The problem statement, all variables and given/known data Problem from the book "Engines, Energy and Entropy", Page 55, question 7 has me stumped. It doesn't feel like their is sufficient information to work out the mass of the air. They've given us density (as seen in the picture, if the upload works) , which is mass over volume, but unless you know the volume of mercury you can't work out the mass from that. Were only given the height of the mercury (maybe in a barometer), But without knowing the area that this height takes. I'm truly stumped on part a), it's not complicated physics. I'm just struggling to see how you can achieve mass if you can't work out volume that the mercury takes up. http://imgur.com/HnOoMAv 2. Relevant equations Ideal gas law as in picture. Density = mass/volume The correct answer is 5.281×1018kg. 3. The attempt at a solution I found the pressure of the mercury (taking T=300K at the surface for a rough estimate) as 167.85 Pa. I don't know how close that is to being correct. I also do not understand the units of R here, what is the L stand for? I also calculated the surface area of the earth as 5.147×1014 m2. But this is useful once I've calculated the mass of the atmosphere. Apologies if it seems like I've not gotten far, I've just spent an hour on it running round in circles and I'm pissed off with it now.