Question

22.Arrange the following molecules in order of increasing average molecular speed. All are at the same temperature.

Answer 1

Slower to fastest

Kr, NO₂,N₂, CH₄

Further explanation

Given

Molecules :

Nitrogen dioxide, Methane, Nitrogen, Krypton

Required

Average molecular speed.

Solution

Average velocities of gases can be expressed as root-mean-square averages. (V rms)  

$\large {\boxed {\bold {v_ {rms} = \sqrt {\dfrac {3RT} {Mm}}}}$

R = gas constant, T = temperature, Mm = molar mass of the gas particles  

So average molecular speed inversely proportional to the molar mass

The larger the molar mass the slower the gas velocity

Molar mass NO₂ = 46 g/mol

Molar mass CH₄ = 16 g/mol

Molar mass N₂ = 28 g/mol

Molar mass Kr = 84 g/mol

slower to fastest :

Kr, NO₂,N₂, CH₄