Calculating the Average Kinetic Energy of a Helium Atom at 20°C

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The average kinetic energy of a helium atom at 20°C can be calculated using the equation E = 3kT/2, accounting for three degrees of freedom in translational kinetic energy. An initial calculation yielded 6.1 x 10^-21 J, but the correct value is 4.0 x 10^-21 J. A simpler approach involves calculating kT directly, which aligns with the correct answer. The discussion highlights a misunderstanding in applying the degrees of freedom in the kinetic energy formula. Clarifying the calculation method is essential for accurate results.
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Homework Statement



What is the average kinetic energy of an atom of helium gas at a temperature of 20 degrees C?


Homework Equations



N/A

The Attempt at a Solution



Here's my attempt at a solution: Using the equation E = kT/2 for each degree of freedom, I found that KE = 3kT/2 since an atom of He has three degrees of freedom in translational KE. Using this logic I fould that KE = 6.1 x 10^-21 while the correct answer should be 4.0 x 10^-21. Can someone help me understand where my logic/reasoning is incorrect? Thanks.
 
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Looks okay to me. Someone got the 4.0 answer by just finding kT.
 
That's what I thought my teacher might have done. Thanks!
 

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