Expert: Tom Whiting - 3/22/2004

Question
-------------------------
Followup To
Question -
Hello Mr. Whiting,
I'm curious about oxygen.
How come oxygen molecules do not all have identically the same speed? and what happens to the average speed and the distribution of speeds when oxygen it is heated?

Thank You
Answer -
Bob,
BTW, Isn't that more of a chemistry or physics
question??  I think so.
tw




After, I tried some of the chemistry "experts", they either delined to help (I don't know why) or didn't respond. You're right though, it is more chemistry, but my professor posed that question in my Astronomy 109 lecture, and started teaching some chem.


Answer
Well Bob,
If I remember my gas laws of physics, any gas, be it
oxygen, nitrogen, chlorine, whatever....are only going
to have an average velocity based on a fixed temperature
and pressure....but due to collisions with other molecules,
the walls of the container, etc, there are some molecules
that, at times, will be below average velocity, and some above average velocity.
I believe any one gas would exhibit the typical 'gaussian-shaped' distribution curve for the various velocities, where say 70% of the oxygen molecules will be within one standard deviation of the mean, 20% will be within two standard deviations, (10% above and below the
mean), and the balance will be at three or more, standard deviations above and below- the mean (average) velocity.

(Maybe that is what your Prof. is looking for, but I just
don't know what he is after..)

Obviously, when heated, it supplies more energy to the
system, so I would think that the average velocity would
increase, thus those molecules whose velocity is above three standard deviations would also increase...and perhaps your instructor is trying to explain how a warmed Earthly atmosphere is trying to explain how on occasion, the Earth can lose some of its O2 to space, and why the lighter gases
that we had some 4 billion years ago, specifically hydrogen
and helium, are long gone....
while the earth retained the "heavies" like nitrogen,
oxygen, carbon dioxide, and a few of the inert gases.

Just a guess on my part, but hope it helps you.
Clear Skies,
Tom Whiting
Erie, PA


PS...Hey, tell him to get "off" the physics, and onto
astronomy....for instance, you want to know the size and
distance of Jupiter (88,000 miles in diameter and 484 million miles from the sun (5.2 AU) and its currently in
the middle of Leo, and is currently high in the east
as darkness falls. And its brightness is -2nd magnitude,
and its 4 largest, brightest moons are Io, Europa,
Ganymede, and Callisto....collectively called the
'Galilean moons'....and it takes Jupiter nearly 12 years to revolve around the sun, and a 'Jovian day' is
9 hr 55 minutes......this is real astronomy!