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P3 Topic 5: Kinetic theory and gases
Kinetic theory and absolute zero
There are three states of matter: solid, liquid and gas. The particles may be the same regardless of state, but
the arrangement of atoms is very different.
Solids: strong forces of attraction hold the particles close together in a fixed, regular arrangement. The
particles don't have much energy so can only vibrate in their fixed positions.
Liquids: These particles are close together but can slide past each other, so have weaker forces of
attraction. As they can move around they have more energy than the particles in a solid.
Gases: There is next to no forces of attraction between particles. The particles have the most energy as they
can move around in random directions at high speeds.
The kinetic theory states gases are made up of very small particles. These particles are constantly moving
and colliding with each other, as well as the walls of their container. When they collide, they bounce of each
other and the walls. The particles hardly take up any space most of it is empty space.
When a substance is cooled down, the kinetic energy of the particles is also being reduced.
In theory, the coldest anything can ever get is -273C. This temperature is known as `absolute zero'. At
absolute zero, the particles are moving as slow as they can get; pretty much still.
Kelvin is measured relative to absolute zero. This means at absolute zero in degrees, there is 0K.
The intervals of 1K and 1C is the same, but their starting point is at different points.
To convert from degrees Celsius to Kelvins = just add 273.
To convert from kelvins to degrees Celsius = just subtract 273.
This means the boiling point of water is 373K and the freezing point of water is 273k.
Pressure, volume and temperature of gases
Kinetic energy is directly proportional to temperature. If you increase the temperature of a gas, it gives it
more energy. `Directly proportional' means if you double the temperature, the average kinetic energy of the
particles also doubles.
The Kelvin temperature of a gas is directly proportional to the average kinetic energy of the particles.
The formula for kinetic energy is: ½ mv2
As gas particles move, they collide with each other and the walls of their container.
When gas particles collide with someone, they exert a force on it. In a sealed container, gas particles smash
against the container's walls, creating an outward pressure.
The pressure depends on how fast the particles are moving and how often they hit the walls.
When a gas is at a constant pressure, its volume is proportional to its temperature.
This means when you heat a gas up, the particles have more kinetic energy and they whizz around faster. The
gas then takes up more room and the volume increases.
When the pressure is constant the volume of a gas before a temperature change is related to its volume
afterwards by this equation:
o Volume1= volume2 x temperature1 (in K)/ temperature2 (in K) V1= V2 X T1 / T2
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V1 and T1 are the starting conditions and V2 and T2 are the final conditions.
Pressure x Volume = Constant
When the temperature if constant, reducing the volume of a gas means the particles get more squashed up
and hit the walls of the container more often, and the pressure increases.
Likewise, if you put the same amount of gas in a bigger container, the pressure will decrease because there
would be fewer collisions between gas particles and the container's walls.…read more