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Pressure in gases

 

 

 

A gas is made up of many isolated particles (atoms or molecules) that are in continuous random motion. That means that as many are travelling in one direction as in the opposite direction - there is no preferred direction.

The are continually colliding with one another and with the walls of the container.

As the gas particles strike and 'bounce off' the walls of the container, they exert a force on the walls - as if they were 'punching' the wall. All these tiny forces add up so that a large number of collisions produces a total average force on the walls that is measurable.

Now, we know that force per unit area is the pressure. Hence, the pressure of a gas is due to the collisions of gas molecules with the walls of the container.

Colliding particles

Gas pressure is caused by gas particles hitting the walls of their container.

The more often the particles hit the walls, and the faster they are moving when they do this, the higher the pressure exerted by the gas.

So:

Increasing the temperature of the gas makes the particles move more quickly. Therefore they hit the container walls more frequently and have more momentum when they do so - therefore the force on the container walls increases, and pressure increases.

Increasing the volume of the conatainer means the particles will hit the walls less frequently (as they have further to travel in between hitting opposite sides). See Boyle's Law.