Two gas questions

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From: Geoff Ruth (gruth@uclink4.berkeley.edu)
Date: Sun Jan 21 2001 - 21:27:22 PST 

Message-Id: <v04011700b691739301cf@[192.168.1.101]>
Date: Sun, 21 Jan 2001 21:27:22 -0800
From: Geoff Ruth <gruth@uclink4.berkeley.edu>
Subject: Two gas questions

Hi, I'm reviewing what I know about gases, and I have a couple questions
that I can't figure out.

1. This first question has been answered many times, but I don't recall an
answer that makes sense to me. If the column of air over my body exerts a
downwards pressure of 14.7 square inches, then why don't I feel it? And why
doesn't my body feel less pressure if I climb to the top of a 14,000 foot
mountain? Is it just a question of getting used to the pressure at the two
places?

2. This second question is more obtuse. I was looking at the volume in L
that 1 mol of different gases occupy. Here are some of the data I saw:
  NH3 22.40 L/mol
  Ar 22.09 L/mol
  He 22.41 L/mol

It makes sense to me that the helium occupies the most volume, since it
would have the smallest van der Waals attraction (least mass). But why
would NH3 not have much stronger intermolecular forces (with dipole-dipole
forces) compared to Ar (only London forces)? I'd expect NH3 to occupy less
space than Ar, not more.

Thanks,
Geoff

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