Question

Can someone just work me through how to do this one problem? I should be OK on the rest then.

Calculate the rms speeds of N2 molecules at 23 degrees C and at 125 degrees C. Sketch the approximate curves of the molecular speed distributions of N2 at 25 degrees C and 125 degrees C.

i know the equation is u= sq root 3RT/Mm but I don't seem to get the right answer.

Answer 1

My work:

At 25 degrees C

u= sq rt. (3 * 8.31 * 298)/(2.80*10^-3km/mol)

u= 16.3 m/s^2

At 125 degrees C

u= sq root (3*8.31*398)/(2.80*10^-3km/mol)

u= 18.8 m/s^2

those answers are wrong. and i don't know how to do the graph

Answer 2

I don't know where the m (the small m) came from. I have
u_rms = sqrt(3RT/M)
You have 3 and R correct in the above equation. The original problem stated 23 degrees but you substituted 298 instead of 296 so you need to check and substitute the correct T. Finally, M is the molar mass in kg, which for N2 is about 0.028 kg but that is 28.0 x 10^-3 instead of the number you have. That's probably the error. Try that and see how it works. I don't know what the question is asking about the graph.