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### Topic: Root mean square speed  (Read 3620 times)

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#### Aakash

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##### Root mean square speed
« on: June 15, 2013, 08:26:54 AM »

There is a question in my book where we have to find root mean square velocity of oxygen at STP provided the density of oxygen. I know the formula that is sqrt3RT/M. But my answer is not coming right and in the solution they have used the formula sqrt(Pressure/density).
« Last Edit: June 15, 2013, 09:35:39 AM by Aakash »

#### Hunter2

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##### Re: Root mean square speed
« Reply #1 on: June 17, 2013, 06:06:41 AM »
Check the units. Only SQR(pressure/density) give a unit for speed.

#### curiouscat

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##### Re: Root mean square speed
« Reply #2 on: June 17, 2013, 06:57:27 AM »
Check the units. Only SQR(pressure/density) give a unit for speed.

No. Other one does too.

#### Hunter2

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##### Re: Root mean square speed
« Reply #3 on: June 17, 2013, 07:29:53 AM »
Yes you are right

#### Nisarg Shah

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##### Re: Root mean square speed
« Reply #4 on: June 17, 2013, 09:48:19 AM »
There is a question in my book where we have to find root mean square velocity of oxygen at STP provided the density of oxygen. I know the formula that is sqrt3RT/M. But my answer is not coming right and in the solution they have used the formula sqrt(Pressure/density).
Most popular formula for RMS speed is vrms=√3RT/M. Using the gas equation and density=mass/volume, you can prove that vrms=√ρ/p (try it yourself), where ρ is the density of the gas.
So both of these equations are the same. This means there is something wrong in your calculations.
Most probable error would be that you've not put the values with correct units.