Question

Arrange the following gases in order of increasing average molecular speed at 25 degrees C: N2, He, O2, CO2

Answer 1

Answer:

Explanation:

For this we're going to take the help of a concept called Graham's law which says

The rate of diffusion of a gas is inversely proportional to the square root of its molar mass

So

Molecular masses of

N2 : 28 g/mole

He: 4 g/mole

O2: 32 g/mole

Co 2 : 44 g/mole

Therefore the order

He>N2>O2>Co2

Answer 2

Explanation:

It is known that relation between average molecular speed and and molar mass is as follows.

    $\frac{R_{1}}{R_{2}} = \sqrt{\frac{M_{2}}{M_{1}}}$

where, $R_{1}$ = average molecular speed of gas 1

             $R_{2}$ = average molecular speed of gas 2

            $M_{1}$ = molar mass of gas 1

            $M_{2}$ = molar mass of gas 2

This means that more is the molar mass of a gas lesser will be its average molecular speed.

Hence, molar mass of nitrogen ($N_{2}$) = 14 g/mol

Molar mass of helium (He) = 2 g/mol

Molar mass of oxygen ($O_{2}$) = 16 g/mol

Molar mass of carbon dioxide ($CO_{2}$) = 44 g/mol

Thus, given gases are arranged in order of increasing average molecular speed at $25^{o}C$ as follows.

        $CO_{2}$ < $O_{2}$ < $N_{2}$ < He