Gases and KE

[casper22]

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While doing the Destroyer 2010, I noticed, one question (Q#21) it says all gases at 1 atm and 25degC have same average Kinetic Energy...

few questions later (Q#38), it says according to the Boltzman curve, at a given temperature molecules of the gas move at different kinetic energy...

I agree with this but what is going on with the 1st question..what am I missing

 

[Expert]

That is correct. All gases at ANY one specific temperature (25 degrees or not) will have the same AVERAGE kinetic energy. The key word is average. This does NOT mean that EVERY gas molecule will have the same exact kinetic energy at a particular temperature. Some molecules will have slightly above average kinetic energy while others will have below average kinetic energy. The kinetic energies of all the molecules are distributed according to the Boltzman curve. But the average kinetic energies of ALL of those molecules will remain constant as long as the temperature is constant. Just because the average KE stays the same does NOT mean that the KE of every molecule is the same. Hope this makes sense.

 

[casper22]

OOOHHH...

Makes sense..Thanks..

 

[spoog74]

That is correct. All gases at ANY one specific temperature (25 degrees or not) will have the same AVERAGE kinetic energy. The key word is average. This does NOT mean that EVERY gas molecule will have the same exact kinetic energy at a particular temperature. Some molecules will have slightly above average kinetic energy while others will have below average kinetic energy. The kinetic energies of all the molecules are distributed according to the Boltzman curve. But the average kinetic energies of ALL of those molecules will remain constant as long as the temperature is constant. Just because the average KE stays the same does NOT mean that the KE of every molecule is the same. Hope this makes sense.

I remember being confused with this as well.

The keyword to watch out for is " average" and dont get fooled if they ask just the temperature. Its the AVERAGE KE thats the same.