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Most Probable Speed - Atoms From An Oven

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Jan20-13, 04:00 PM
P: 17
Hi there,

I'm looking to find the most probable speed of atoms ejected from an oven.

Temp (T) is 900C (so 1173.15K).

The material is aluminium with molar mass 0.027kg mol-1

I've got the formula vmp=√(2kT/m)

I'm fine with everything above, but I'm not sure what value to use as the Boltzmann constant k.

Can anyone please help me here? Do I have the right equation and what value for the constant should I use (sounds silly, but it changes depending upon units. I've tried a couple but get silly tiny speeds out. I think I should expect something in the region of a few hundred metres per second).

Many thanks

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Jan20-13, 04:37 PM
Sci Advisor
HW Helper
P: 7,274
In SI units:
K = 1.38e-23 J/K
m = mass of one molecule = 0.027/6.022e23 kg
T = 1173 K

... which gives a velocity of "hundreds of m/s" as you expected.

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