Gas PressureGas Pressure

D. Crowley, 2007D. Crowley, 2007

Gas PressureGas PressureTo understand what causes gas pressureTo understand what causes gas pressure

Wednesday, April 19, 2023

DiffusionDiffusion Look at the diagram which shows bromine gas and air

contacting each other. The models show the direction the particles take - which one is

correct?

Look at the diagram which shows bromine gas and air contacting each other.

The models show the direction the particles take - which one is correct?

Bromine

Air The cover was removed, and after about an hour the glass jar looked like this

Cover

Model 1 Model 2 Model 3

DiffusionDiffusion Diffusion is the net movement of particles from an area of high

concentration, to an area of low concentration So the particles gradually move from where there are lots of

them, to areas where there are less (net just means the overall) It’s a bit like lots of football fans leaving a stadium after a game.

At the stadium they are in a high concentration, but as they leave, they ‘diffuse’ into the streets and travel home, to where there are less football fans (low concentration)

Diffusion is the net movement of particles from an area of high concentration, to an area of low concentration

So the particles gradually move from where there are lots of them, to areas where there are less (net just means the overall)

It’s a bit like lots of football fans leaving a stadium after a game. At the stadium they are in a high concentration, but as they leave, they ‘diffuse’ into the streets and travel home, to where there are less football fans (low concentration)

Diffusion - net movement from a high concentration to a low concentration

TyresTyres When you ride your bike its important to have your tyres

pumped up - but why do you do this? Has anyone ever ridden over bumpy ground with flat tyres?

What was it like? Pumping up your bike tyres cushions you against bumps when

you ride, and this is all because of gas pressure…

When you ride your bike its important to have your tyres pumped up - but why do you do this?

Has anyone ever ridden over bumpy ground with flat tyres? What was it like?

Pumping up your bike tyres cushions you against bumps when you ride, and this is all because of gas pressure…

BalloonBalloon Draw an outline of a balloon - can you draw the particles, and explain

what is going on? Why does the balloon keep its shape when you blow it up? Why does it

loose its shape after a few days? Why can it pop if you blow it up too much?

Draw an outline of a balloon - can you draw the particles, and explain what is going on?

Why does the balloon keep its shape when you blow it up? Why does it loose its shape after a few days? Why can it pop if you blow it up too much?

BalloonBalloon Draw an outline of a balloon - can you draw the particles, and explain what is

going on? Why does the balloon keep its shape when you blow it up? Why does it loose its

shape after a few days? Why can it pop if you blow it up too much?

Draw an outline of a balloon - can you draw the particles, and explain what is going on?

Why does the balloon keep its shape when you blow it up? Why does it loose its shape after a few days? Why can it pop if you blow it up too much?

Air is a gas. When you blow a balloon up, many gas particles get trapped inside.

The particles move around quickly and randomly, but they often collide with other gas particles, as well as the side of the balloon.

When these gas particles hit the side of the balloon they cause pressure. The more these particles hit the side, the greater the pressure becomes.

This is why when you pump up a tyre too much, or blow a balloon up too much, it can burst - you’ve caused too many particles to crash into the side of the tyre / balloon, causing the pressure to get too high!

Eventually the balloon will shrink - this is because they are not completely air tight. As air escape, the pressure decreases as less particles are colliding with the sides (and it shrinks)

Gas pressureGas pressure Gas pressure causes a balloon / tyre to keep its shape

The pressure is caused by the trapped gas particles colliding into the sides of the container they are in

The more particles there are in there, the greater the pressure becomes (until you try to put too many particles in, when often the balloon pops)!

Gas pressure causes a balloon / tyre to keep its shape

The pressure is caused by the trapped gas particles colliding into the sides of the container they are in

The more particles there are in there, the greater the pressure becomes (until you try to put too many particles in, when often the balloon pops)!

Gas particles hit the wall of their container, causing pressure

HeatHeatWhat about heat?

Two balloons, of equal size, will experience different temperatures - one will be placed in some warm water, the other in cold water…

What do you think will happen to the particles inside the balloon if it is heated?(hint: think about what the gas particles do when they get hot)

What do you think will happen to the particles inside if the balloon is cooled?

If a gas is heated up, its particles move around more quickly. They will hit the sides of the balloon harder, and more often. This will then increase the pressure (and the balloon expands)

The opposite happens when you cool it - the particles move slower, crash into the sides with less force, and less often, decreasing the pressure (so the balloon shrinks)

What about heat?

Two balloons, of equal size, will experience different temperatures - one will be placed in some warm water, the other in cold water…

What do you think will happen to the particles inside the balloon if it is heated?(hint: think about what the gas particles do when they get hot)

What do you think will happen to the particles inside if the balloon is cooled?

If a gas is heated up, its particles move around more quickly. They will hit the sides of the balloon harder, and more often. This will then increase the pressure (and the balloon expands)

The opposite happens when you cool it - the particles move slower, crash into the sides with less force, and less often, decreasing the pressure (so the balloon shrinks)

Custard bomb…Custard bomb… So why do balloons and tyres pop if you put too much air in? Why do aerosol

cans explode when they get hot?

Blow up a balloon too much and you’ll have so many particles hitting the side of it that the pressure will be too great - causing the balloon to pop.

If a gas is heated up, its particles move around more quickly. They will hit the sides of the container harder, and more often. This will then increase the pressure - heat it up too much, and you’ll create too much pressure inside, causing the container to explode.

So why do balloons and tyres pop if you put too much air in? Why do aerosol cans explode when they get hot?

Blow up a balloon too much and you’ll have so many particles hitting the side of it that the pressure will be too great - causing the balloon to pop.

If a gas is heated up, its particles move around more quickly. They will hit the sides of the container harder, and more often. This will then increase the pressure - heat it up too much, and you’ll create too much pressure inside, causing the container to explode.

Gas PressureGas Pressure Complete gas pressure 1 - stick this into you book… Complete gas pressure 1 - stick this into you book…

Gas PressureGas Pressure Get your neighbours book, and mark

the answer in - 1 mark per correct answer…

1) The particles in a gas are moving around all the time. The particles bump into the sides of their container. The force of the particles hitting the sides causes pressure. If you put more particles into a container, there will be more particles to collide with the walls, and the pressure will increase

2a) The air pressure inside will decrease (less particles colliding into the container)

2b) The bottle will collapse inwards because the pressure on the outside (pushing the bottle in) is now much greater than the pressure on the inside (pushing the bottle out).

Get your neighbours book, and mark the answer in - 1 mark per correct answer…

1) The particles in a gas are moving around all the time. The particles bump into the sides of their container. The force of the particles hitting the sides causes pressure. If you put more particles into a container, there will be more particles to collide with the walls, and the pressure will increase

2a) The air pressure inside will decrease (less particles colliding into the container)

2b) The bottle will collapse inwards because the pressure on the outside (pushing the bottle in) is now much greater than the pressure on the inside (pushing the bottle out).