# RMS speeds of helium and argon atoms

1. Aug 23, 2008

### twiztdlogik

i am having a bit of trouble with this question, and its not explained very clearly in our text book...

"what are the RMS speeds of helium an dargon in a gas at 1000 degrees C"

any help would be greatly appreciated. physics is definately not one of my strengths...

=D

cheers.
KC

2. Aug 23, 2008

### dynamicsolo

You will want to use the formula for the root-mean-square speed of molecules in an ideal gas

$$v_{rms} = \surd \frac{3kT}{m}$$

where k is the Boltzmann constant, T is the absolute temperature in Kelvins (so you will have to convert the 1000º C.), and m is the molecular mass in kg. (you will need the mass of a helium or argon atom in atomic mass units and the value for 1 amu in kilograms).

3. Aug 23, 2008

### twiztdlogik

oh thanks a bunch!! ur a genius

4. Aug 23, 2008

### dynamicsolo

I am going to reply that you can be as big a "genius" as I was to answer this. As they like to say around various forums, Google is your friend. I searched on "molecular speeds" and "RMS" to make sure I gave you the right formula; there are three averages given for speeds in velocity distributions of molecules in an ideal gas, all with similar expressions and differing only in the numerical constant... (The 'Net is an excellent reference source for physics material, if you don't mind having to pick through search results.)