1. Gas Pressure
D. Crowley, 2007

2. Gas Pressure To understand what causes gas pressure
Tuesday, November 20, 2018
To understand what causes gas pressure

3. Diffusion
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?
Air
The cover was removed, and after about an hour the glass jar looked like this
Cover
Bromine
Model 1
Model 2
Model 3

4. Diffusion
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

5. Tyres
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…

6. Balloon
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?

7. Balloon
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)

8. Gas 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 particles hit the wall of their container, causing pressure

9. Heat
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)

10. 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.

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

12. Gas Pressure
Get your neighbours book, and mark the answer in - 1 mark per correct answer…
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).