Question

Part A

 Place the following gases in order of decreasing average molecular speed at 29 °C: Ne, HBr, SO2, NF3, CO.

 Part B

 Calculate the rms speed of NF3 molecules at 29 °C.

Answer 1

A)

vrms = sqrt (3*R*T/M)

here : T is temperature in Kelvin

M is molar mass

vrms = sqrt (3*R*T/M)

here : T is temperature in Kelvin

M is molar mass

Since T is same for all, the one with lower molar mass will have higher speed

Lets list out molar mass of all given compounds

Molar mass of Ne = 20.18

Molar mass of HBr = 80.908

Molar mass of SO2 = 64.07

Molar mass of NF3 = 71.01

Molar mass of CO = 28.01

Increasing order of molar mass is:

Ne

CO

SO2

NF3

HBr

Same is the order of decreasing vrms

From fastest to slowest

Ne

CO

SO2

NF3

HBr

Ne > CO > SO2 > NF3 > HBr

B)

Molar mass of NF3,

mm = 71.01g/mol

= 0.07101 Kg/mol

T= 29.0 oC

= (29.0+273) K

= 302 K

vrms = sqrt (3*R*T/M)

here : T is temperature in Kelvin

and M is molar mass in Kg/mol

So,

vrms = sqrt(3*8.314*302.0/0.07101)

= 326 m/s

Answer: 326 m/s