RMS speed of Hydrogen Atoms in space

[notsam]

Homework Statement

In outer space the density of matter is about one atom per cm^3, mainly hydrogen atoms , and the temperature is about 2.7 K. Calculate the rms speed of these hydrogen atoms, and the pressure (in atmospheres).

Homework Equations

.5mv^2 = 3/2 KT

The Attempt at a Solution

PLEASE HELP! :) Ok so I have all knowns EXCEPT mass to I get that from my density? Using whatever hydrogens molecular mass is?

 

[Fewmet]

Homework Equations

.5mv^2 = 3/2 KT

The Attempt at a Solution

PLEASE HELP! :) Ok so I have all knowns EXCEPT mass to I get that from my density? Using whatever hydrogens molecular mass is?

I use a variation of the formula in my teaching. Oxtoby, Gillis and Nachtrieb have a good derivation. I'm not sure if http://books.google.com/books?id=kX...onepage&q=the meaning of temperature&f=false" will work for you. If not, search Google Books for the authors. The text is Principles of Modern Chemistry. It is on page 379 of the sixth edition.

It ends with v_rms=\sqrt{3RT/M}
where R = 8.3145 kg m²/s²-mol-K
and M is the molecular mass in kg/mol

I am pretty sure the equation you gave will work using the mass of H (1.0079 atmic mass units) in the appropriate units.