Question

What causes pressure in a closed container of gas?

Answer 1

Collisions between the gaseous molecules and the walls of the container, and collisions between the molecules.

Explanation:

At a molecular level, the gaseous particles impact the walls by collision, and the `"force per unit area"` exerted on the the container by the gas is the `"pressure"`.

Gas laws that relate pressure and temperature for a given volume or given quantity of gas, were perfected and rationalized very quickly, and it allowed early chemists and physicists to have a very shrewd idea of molecular properties, even though they had no way to measure the molecules (but for their macroscopic pressure, and temperature, and volume).