Chemistry
posted by Lydia .
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

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. 
thanks

so is it
3 x 8.314 x (16°C + 273)K / (146.065 molecules / 6.02e23) = 2.970841253e25 ?
is that right? 
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). 
ok so...
sqrt(3 x 8.314 x 289/146.056) = 7.025 m/s
is that right? 
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).