Chemistry
posted by Hannah .
Which molecule below has the greatest average velocity at 100 degrees celsius?
He, Cl2, Xe, O2, NO2
I know that I already posted this the other day and the response I was given was to use the root mean squared equation. I know that the molecule with the smallest mm will be the fastest and I used the root mean squared equation but I think I did it wrong. The answer I chose was Xe as the greatest because I came up with 0.0076 but now I am confused and do not think I did this right. The regular mm of Xe is the biggest number out of all the answers so then Xe would not be the answer.
Could someone please just make sure I did this correct? Thank you!!

I gave you the rms speed earlier; I thought that might be easier to handle but the answer you get should be the same as the kinetic energy calculation. The average kinetic energy of a molecule is 1/2 mv^2 and the average KE of different molecules is the same at the same T.
So if KE is the same for all of the molecules, then
KE = 1/2 mv^2 where v is the average speed of the molecules.
If we solve for v, we obtain v = sqrt(2*KE/m).
Look at the equation. m is in the denominator which means v is indirectly proportional to m. So the heaviest molecule will have the least average velocity; the lightest molecule will have the highest average speed. Which is the heaviest molecule? which is the lightest molecule? You don't need to do any calculations. T is a constant for all of these, the only variable is molar mass so v = k*sqrt(1/M). 
Is K the temp in kelvins?
So for an example He would be
373K(sqrt 1/4.0026) = 186.43
Did I do that right? 
I don't know to what you refer. K in KE stands for kinetic energy. Don't obsess about this. rms speed He = sqrt(3RT/M) = sqrt(3*8.314*373/4) = ?
rms speed Xe = sqrt(3*8.314*373/131.3) = ?
The others are done the same way and you simply pick out the greatest rms speed. That isn't the average speed but it will do. For average speed one uses the kinetic energy.
However, note that you do NOT need to do any calculations.
If kinetic energy = KE = 1/2 mv^2, then
v = average speed = sqrt(2*KE/mass)
so highest mass = lowest speed
lowest mass = highest speed. That's all there is to it. 
ok so the lowest mass is Xe and the highest mass is NO2.
Respond to this Question
Similar Questions

urgent
How much heat energy is required to raise the temp of 5 kilograms of coal from 20 degrees celsius to 220 degrees celsius? 
chemistry
Which of the following equations correctly describes the relationship between the rate at which NO2 and Cl2 are consumed in the following reaction? 
science
Which of the following equations correctly describes the relationship between the rate at which NO2 and Cl2 are consumed in the following reaction? 
Chemistry
Which molecule below has the greatest average velocity at 100 degrees celsius? 
Chemistry
Which molecule has the greatest average velocity at 100 degrees celsius. He, Cl2, Xe, O2, NO2 I used the root mean squared formula but I think I did it wrong. I got Xe as my answer. Is this correct? 
Chemistry(Please help, thank you!)
Using this data, 2 NO(g) + Cl2(g) == 2 NOCl(g) Kc = 3.20 X 103 NO2(g) == NO(g) + ½ O2(g) Kc = 3.93 calculate a value for Kc for the reaction, NOCl (g) + ½ O2 (g) == NO2 (g) + ½ Cl2 (g) I do not understnad how I am suppose to use … 
Chemistry(Please respond, thank you!)
Using this data, 2 NO(g) + Cl2(g) == 2 NOCl(g) Kc = 3.20 X 103 NO2(g) == NO(g) + ½ O2(g) Kc = 3.93 calculate a value for Kc for the reaction, NOCl (g) + ½ O2 (g) == NO2 (g) + ½ Cl2 (g) So I understand that 2NO + Cl2 + 1/2O2 = NO2 … 
Chemistry
the reaction 2 NO + O2 <=> 2 NO2 (delta H = 114.2 kJ) has a Kc=7.00 x 10^7 at 200 degrees Celsius. what is the value of Kc at 400 degrees celsius? 
Chemistry
Consider the reaction for the production of NO2 from NO: 2 NO(g) + O2(g) = 2 NO2(g) a)If 84.8L of O2(g), measured at 35 degrees Celsius and 632mm Hg, is allowed to react with 158.2g of NO, find the limiting reagent. b) If 97.3L of … 
chemistry
arrangement of the following gas molecule in their increasing average speed at the same temperature. O2, N2, H2O,CO2,NO2 and Cl2