Why do heaviest molecules have lowest rms speed?

[SaintJude]

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Why do the heaviest molecules have the smallest root means square speed?

 

[dmf2682]

Why do the heaviest molecules have the smallest root means square speed?

Not entirely sure without a context but intuitively it would make sense. For a given energy level kinetic energy is .5 m v2 so if m goes up v drops.

 

[SaintJude]

You're confusing rms speed given by the energy of a single particle with the average kinetic energy of an entire ideal gas.

Edit: Or maybe you're not? Hmm.

 

[pm1]

Why do the heaviest molecules have the smallest root means square speed?

Why do the heaviest molecules have the smallest root means square speed?

I don't know if you are familiar with the formula Vrms = sort (3RT/M) ??

but you might want more of a theoretical explanation. I can't say much but I can talk about the problems that I usually get related to this - it is usually referring to effusion rate, which is proportional to Vrms speed.

Usually they are comparing molecules that are under the same temperature. Hence, their kinetic energy must be the same.

mv^2/2 of molecule 1 = mv^2/2 of molecule 2

then you can get to the V1/V2 = sqrt m2 / sqrt m1 . The bigger the mass, the smaller the Vrms.

I hope I'm in the right track, and that it actually helps you a little 😀

 

[theseeker4]

I don't know if you are familiar with the formula Vrms = sort (3RT/M) ??

but you might want more of a theoretical explanation. I can't say much but I can talk about the problems that I usually get related to this - it is usually referring to effusion rate, which is proportional to Vrms speed.

Usually they are comparing molecules that are under the same temperature. Hence, their kinetic energy must be the same.

mv^2/2 of molecule 1 = mv^2/2 of molecule 2

then you can get to the V1/V2 = sqrt m2 / sqrt m1 . The bigger the mass, the smaller the Vrms.

I hope I'm in the right track, and that it actually helps you a little 😀

This sounds right to me. In a mixture of gasses, the mixture is at a single temperature, which means the average kinetic energy of each component is the same. The lighter the molecule, the faster it must be moving to have the same kinetic energy.

 

[gettheleadout]

This sounds right to me. In a mixture of gasses, the mixture is at a single temperature, which means the average kinetic energy of each component is the same. The lighter the molecule, the faster it must be moving to have the same kinetic energy.

This is similar to the way I thought about it when I read the thread title. Comparing Vrms between different molecules in the same container means the temperature is the same, so a heavier molecule won't be able to move as fast with an equal amount of energy compared to a lighter one.

 

[MedPR]

Why do the heaviest molecules have the smallest root means square speed?

Why would a heavier molecule move faster than a lighter molecule?

 

[milski]

Why would a heavier molecule move faster than a lighter molecule?

Because it's harder to slow it down? 😛

 

[gettheleadout]

Because it's harder to slow it down? 😛

What sucks is when you start to doubt yourself with logic like this. 😀

 

[milski]

What sucks is when you start to doubt yourself with logic like this. 😀

He's done with the MCAT, it's fair game to mess with him now. 😎

 

[MedPR]

Because it's harder to slow it down? 😛

What sucks is when you start to doubt yourself with logic like this. 😀

Yea, well I'm done so I don't really care why 😀.

 

[gettheleadout]

He's done with the MCAT, it's fair game to mess with him now. 😎

When's your date milski?

 

[milski]

When's your date milski?

Jan/2013. I'm a slacker. 😎 You?

 

[gettheleadout]

Jan/2013. I'm a slacker. 😎 You?

April after yours haha, I'm just getting practice in checking out problems on here a year in advance.

 

[milski]

April after yours haha, I'm just getting practice in checking out problems on here a year in advance.

No writing section FTW! 👍

I dropped in for the same reason. Explaining physics problems turned out to be addictive.

 

[gettheleadout]

No writing section FTW! 👍

I dropped in for the same reason. Explaining physics problems turned out to be addictive.

Dude! I found out about the early dropping of the WS just the other day and was so happy haha...

You definitely have a profound skill with physics. Are you a physics major?

 

[milski]

Dude! I found out about the early dropping of the WS just the other day and was so happy haha...

You definitely have a profound skill with physics. Are you a physics major?

I know that it barely matters but I'm just happy that I don't have to do it. Writing is always painful for me and I'm borderline mediocre - it's good to know that we'll be able to avoid this hoop.

Yes, I am a physics major. Although one of the major reasons I picked it was because I found physics relatively easy and logical. I'd probably do better with math but I find it mind-numbingly boring.

 

[MedPR]

There's no writing section in 2013??

 

[milski]

There's no writing section in 2013??

Correct. They finally admitted that it's useless. Instead we'll get some experimental questions in the new areas that are going to be present on the 2015 MCAT. Participation for that section is optional, the results are not reported and supposedly there is some sort of benefit for those who chose to take it. Lots of details are still unknown but there's almost a year until then.

 

[MedPR]

Correct. They finally admitted that it's useless. Instead we'll get some experimental questions in the new areas that are going to be present on the 2015 MCAT. Participation for that section is optional, the results are not reported and supposedly there is some sort of benefit for those who chose to take it. Lots of details are still unknown but there's almost a year until then.

Ah, well for better or worse, I'm glad I'm done. I don't like changes, even if the ultimately make the MCAT easier. I agree that answering questions on here is a addicting, so I anicipate being around for a while. That said, I certainly won't be doing any kind of research to answer PS questions I don't already know. I'll leave that to you PS pros.