Rms speed of Hydrogen atoms in space

AI Thread Summary
The discussion focuses on calculating the root mean square (rms) speed of hydrogen atoms in outer space, where the density is approximately one atom per cm³ and the temperature is around 2.7 K. The equation PV = NkT is referenced, but the user is uncertain about how to determine the volume needed for the calculation. The equipartition theorem is mentioned, indicating that hydrogen atoms possess kinetic energy related to their temperature and degrees of freedom. The user seeks clarification on what mass to use for hydrogen atoms in their calculations. Overall, the thread revolves around applying thermodynamic principles to find the rms speed and pressure of hydrogen in space.
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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

PV = NkT




The Attempt at a Solution

So by using PV = NkT, I have all the variables except the volume. Or am I way off using this equation.
 
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Have you encountered the equipartition theorem before? According to the theorem, hydrogen atoms have a kinetic energy of 3/2kT, because they have 3 degrees of freedom.
 
Ok...so 1/2(mv^2)=3/2kT. But what do I use for mass?
 

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