Can you help me with problem on average molecular speed?

Question

How do I calculate and arrange the average molcular speeds of Cl2, O2, and F2, and N2 in increasing order?

Answer 1

You need to know the absolute temperature T of the gases.  Assuming they are all at the same temperature and assuming all of the kinetic energy of the gas is translational kinetic energy,

 

(1/2)mv_rms² = (3/2)kT

 

where k is the Boltzmann constant, and m is the mass of one gas molecule.

 

v_rms = √(3kT/m)

 

Note that at the same temperature, a gas of high molecular mass will have low rms speed, and a gas of low molecular mass will have high rms speed.