# Physics - P3

Kinetic Theory, Pressure in Gases, the Kelvin Scale and Gas Laws.

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• Created by: Tiula
• Created on: 03-04-10 09:55

## Kinetic Theory

Kinetic Theory states that gases consist of very small particles that are constantly moving in random directions. These particles are continually colliding with one another and with the walls of their container.

At lower temperatures, the particles have less energy, so they move around less. At absolute zero (-273 C or 0 K) particles stop moving altogether.

Kinetic energy of the particles in a gas is directly proportional to its temperature (in K)

=> this is a fancy way of saying "double the temperature in Kelvins, double the kinetic energy".

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## The Kelvin Scale

The Kelvin scale is very similar to Centigrade, but the zero is in a different place.

Absolute zero -273 C 0 K

Water freezes 0 C 273 K

Water boils 100 C 373 K

To transfer from Kelvin to Centigrade, subtract 273.

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## Particles in Gases

When gases move around, they are colliding with the walls of their container and with each other. When they collide, the exert a force, creating pressure.

If you heat a gas, the particles have more energy and so they move faster, this means that they collide more often and with greater force, so the pressure is increased.

If you squish a gas, the particles are closer together, so they collide more often, so pressure is increased.

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## Gas Laws

( Pressure x Volume ) / Temperature = constant

so:

( P x V ) / T = ( p x v ) / t

e.g.:

a gas at pressure 2.5 atmospheres is compressed from 300 cm to 175 cm. This makes the temperature increase from 230 K to 280 K. Find the new pressure.

( 2.5 x 300 ) / 230 = ( p x 175 ) / 280

p = 5.22 atmospheres

REMEMBER: TEMPERATURE MUST ALWAYS BE IN KELVIN!

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