Derive the equation of $v_{rms}$ in terms of the mass of a molecule.

Vedclass pdf generator app on play store
Vedclass iOS app on app store
(N/A) The average kinetic energy of one molecule of an ideal gas is given by:
$<\frac{1}{2} m v^{2}> = \frac{3}{2} k_{B} T$
Where $m$ is the mass of the molecule,$v$ is the velocity,$k_{B}$ is the Boltzmann constant,and $T$ is the absolute temperature.
Rearranging the equation for the mean square velocity $\langle v^{2} \rangle$:
$\langle v^{2} \rangle = \frac{3 k_{B} T}{m}$
The root mean square velocity $v_{rms}$ is defined as the square root of the mean square velocity:
$v_{rms} = \sqrt{\langle v^{2} \rangle} = \sqrt{\frac{3 k_{B} T}{m}}$
From this expression,it is evident that for a given temperature $T$:
$v_{rms} \propto \frac{1}{\sqrt{m}}$
Thus,at a constant temperature,lighter molecules possess higher root mean square speeds compared to heavier molecules.

Explore More

Similar Questions

Given below are two statements:
Statement $I$: The average momentum of a molecule in a sample of an ideal gas depends on temperature.
Statement $II$: The rms speed of oxygen molecules in a gas is $v$. If the temperature is doubled and the oxygen molecules dissociate into oxygen atoms,the rms speed will become $2v$.
In the light of the above statements,choose the correct answer from the options given below.

For a gas,the $r.m.s.$ speed at $800 \, K$ is

At temperature $T$,$N$ molecules of gas $A$ each having mass $m$ and at the same temperature $2N$ molecules of gas $B$ each having mass $2m$ are filled in a container. The mean square velocity of molecules of gas $B$ is $v^2$ and the mean square of the $x$-component of velocity of molecules of gas $A$ is $w^2$. The ratio of $w^2/v^2$ is:

Difficult
View Solution

The speeds of gas molecules are $2, 3, 4, 5, 6 \ km/s$. The $rms$ speed is ............. $km/s$.

Difficult
View Solution

$A$ mixture of $2$ moles of helium gas (atomic mass $= 4 \ amu$) and $1$ mole of argon gas (atomic mass $= 40 \ amu$) is kept at $300 \ K$ in a container. The ratio of the rms speeds $\left(\frac{v_{\text{rms}} \text{ (helium)}}{v_{\text{rms}} \text{ (argon)}}\right)$ is:

Vedclass Products

For Students

Vedclass Test Series

Mock tests in real JEE/NEET style with performance analysis. 5-day free trial.

Start Free Trial
For Teachers

Exam Paper Generator

Generate Set A/B/C/D exam papers from 7.5L+ questions in 2 minutes. 3 chapters free.

Try Free
For Institutes

Online Exam Module

Live online exams with unlimited students, 360° analytics & white-label branding.

See Demo