Posted by **Lydia** on Sunday, May 17, 2009 at 9:59pm.

I have no clue as to how this problem should be solved... could i have some help please?

Calculate the rms speed of SF6 molecules at 16°C

- Chemistry -
**DrBob222**, Sunday, May 17, 2009 at 10:12pm
The formula is in your text, I'm sure. Look under Kinetic Molecular Theory.

rms = sqrt(3RT/M) where R is 8.314, T is is Kelvin and M is molar mass.

- Chemistry -
**Lydia**, Sunday, May 17, 2009 at 10:15pm
thanks

- Chemistry -
**Lydia**, Sunday, May 17, 2009 at 10:26pm
so is it

3 x 8.314 x (16°C + 273)K / (146.065 molecules / 6.02e23) = 2.970841253e25 ?

is that right?

- Chemistry -
**DrBob222**, Sunday, May 17, 2009 at 11:07pm
No. You have omitted the square root AND you stuck a 6.02e23 in there that doesn't belong there.

rms = sqrt(3*8.314*289/146.056) = ??

The M is the molar mass; i.e., the mass of 1 mol which is 146.056g (not 146.065 molecules).

- Chemistry -
**Elizabeth**, Sunday, May 17, 2009 at 11:12pm
ok so...

sqrt(3 x 8.314 x 289/146.056) = 7.025 m/s

is that right?

- Chemistry -
**DrBob222**, Sunday, May 17, 2009 at 11:18pm
That's what I have. If your prof is picky about significant figures, I would round the 7.025 to 7.02 m/s (three places since the 289 is to 3 places).

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