Two identical flasks contain O_{2} and H_{2} gas, respectively, at the same temperature and pressure. In comparing the two flasks, which of the following is not a true statement.

(a) the average kinetic energy of H_{2} is greater than that of O_{2}

(b) the average speed of a H_{2} molecule is greater than that of an O_{2}

(c) the number of impacts/(unit area)/(unit time) are different for the two gases

(d) the number of moles is the same

(e) total mass of each gas is different

We are asked **which of the statements are NOT TRUE given: **

Two identical flasks contain O_{2} and H_{2} gas, respectively, at the same temperature and pressure.

**Analyze each statement:**

**(a) the average kinetic energy of H _{2} is greater than that of O**

- The temperature is the same so the average kinetic energy is the same.
**H**_{2}is lighter than O_{2}so this is FALSE.

**(b) the average speed of a H _{2} molecule is greater than that of an O**

Recall that the ** molecular speed of a gas** is given by:

$\overline{){\mathit{m}}{\mathit{o}}{\mathit{l}}{\mathbf{.}}{\mathbf{}}{\mathit{s}}{\mathit{p}}{\mathit{e}}{\mathit{e}}{\mathit{d}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}\sqrt{\frac{\mathbf{3}\mathbf{R}\mathbf{T}}{\mathbf{M}}}}$

where **R** = gas constant, **T** = temperature, and **M** = molar mass of the gas.

- We can see that the molar mass is in the denominator.
- This means that the lower the molar mass the faster the molecule is.
**H**_{2}is lighter than O_{2}so this is TRUE.

Kinetic Molecular Theory

Kinetic Molecular Theory

Kinetic Molecular Theory

Kinetic Molecular Theory