Kinetic Theory

P3 Unit 3 Physics Edexcel Topic 5 Particles in action

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  • Created by: Elouise
  • Created on: 03-04-12 09:36

Basics Refresher on Gas:

Gas consists of very small particles that move in random directions.

They collide with other particles & the walls of the container & bounce off when they do.

They take up hardly any space.

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Absolute Zero

Increasing the temperature of a substance gives the particles more energy so they move more quickly or vibrate more. If you cool the substance down you reduce the kinetic energy.

The coldest anything can be - absolute 0 - is -273 degrees Celsius. This starts the Kelvin scale so -273 degrees Celsius - 0 Kelvin.

Celsius -> Kelvin = Add 273

Kelvin -> Celcius = Subtract 273.

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Kinetic energy is proportional to temperature.

Increase Temperature = More Energy

Double Temperature (Kelvin) = Double the average Kinetic Energy

When you heat up a gas the average speed of the particles increases. Anything that is moving has kinetic energy.

Kinetic energy = 1/2mv^2 (0.5 x mass x (velocity squared) ) 

IMPORTANT: When calculating kinetic energy, remember to only square the velocity, not the whole answer!

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Pressure in gases

Gas particles are light but they do have a mass, this means when they collide with something, they exert a force.

In a sealed container the gas particles hit the containers walls and create an outward pressure.

The pressure depends on how fast the particles are going and how often they collide and hit the walls.

An increase in kinetic energy due to an increase in temperature means they hit harder against the walls of the container so create more pressure. 

Temperature and pressure are proportional.

If you put the same volume of gas in a bigger container there will be less pressure. A smaller container with the same volume of gas will create more pressure. This is because there is less space so they will collide more often with the walls of the container.

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Constant in a Sealed Container


____________________      =     Constant

 Temperature (in Kelvin)




P/T = Constant 


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    Pressure x Volume

____________________      = Constant

 Temperature (in Kelvin)



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