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Unit P3 ­ Topic 1 ­ Particles in Action…read more

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Kinetic Theory and Temperature in Gases
Specification Point: 1) The term absolute zero, -273°C, in terms of the lack of movement of
particles. 2) The Kelvin scale of temperature and be able to convert between the Kelvin and
Celsius scales. 3) The effect of changing the temperature of a gas on the speed of its particles.
Kinetic Energy Says Gases are Randomly Moving Particles
1) Kinetic theory says that gases consist of very small particles.
2) These particles are constantly moving in completely random directions
3) They constantly collide with each other and the walls of their container. When they collide,
they bounce off each other, or off the walls
4) The particles hardly take up any space. Most of gas is empty space.
Absolute Zero is the coldest temperature possible
If you increase the temperature of something, you give it more energy ­ the particles move
around quicker and vibrate more. In the same way, if you cool a substance down you are
reducing the amount of kinetic energy of the particles making them slower.
The coldest that anything can ever get is -273C ­ this temperature is known as absolute zero.
At absolute zero, atoms have the smallest amount of kinetic energy possible.
Absolute zero is the start of the Kelvin scale of temperature,
A temperature change of 1 C is also a change of 1 Kelvin. The scales are pretty similar ­ the
only difference is where the zero occurs.
To convert from Celsius to Kelvins, just add 273. And to convert from Kelvins to Celsius, just
subtract 273.…read more

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Specification Point: Relate the Kelvin temperature of a gas to the average kinetic energy of
its
particles (direct proportionality)
Kinetic Energy is Proportional to Temperature
1) If you increase the temperature of a gas you give it more energy.
2) In fact if you double the temperature (measured in Kelvin) you double the average
kinetic energy of the particles.
The temperature of a gas (in Kelvin) is proportional
To the average kinetic energy of its particles.
As you heat up a gas, the average speed of its particles increases. Anything that's moving (such
as particles) has kinetic energy.
Kinetic energy = ½ x Mass x Velocity2
K.E.
½xMxV…read more

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Kinetic Theory and Pressure in Gases
Specification Point: the pressure of a gas in terms of the motion of its particles
Kinetic Theory says Colliding Gas Particles Create Pressure
As particles move about, they bang into each other and whatever else that happens to get in
the way.
Gas particles are very light but they are not massless. When they collide with something,
they exert a force on it. In a sealed container, gas particles smash against the container's
walls ­ creating an outward pressure.
This pressure depends on how fast the particles are going and how often they hit the walls.
If you heat a gas, the particles move faster and have more kinetic energy. This increase in
kinetic energy means the particles hit the container walls harder and more often, creating
more pressure.
And if you put the same amount of gas in a bigger container, the pressure will decrease, as
there will be fewer collisions between the gas particles and the container's walls. When the
volume is reduced the particles are more squashed and so they hit the walls more often,
hence the pressure increases.…read more

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Made by Esta Finesilver
Specification Point: use the equation for a gas in a sealed container, the ratio:
Pressure/Temperature (Kelvin) = constant P/T = constant
In a sealed container Pressure = Constant P = Constant
(i.e. constant volume): Temperature (in K) T
You can also write the equation as P1/T1 = P1/T1 (where P1 and T1 are your starting conditions
and P2 and T2 are your final conditions) Preferred method most of the time.
Example: A container has a volume of 30 litres. It is filled with gas at a pressure of 1atm a
temperature of 290K. Find the new pressure if the temperature is increased to 315K
Answer: P1/T1 = P2/T2 gives 1 / 290 = P2 / 315 so P2 = 315 /290 = 1.09 atm
NB. The temperature in this formula must always be Kelvin so if they give you the temperature
in Celsius convert it to Kelvin FIRST. Always keep the pressure units the same as they are in the
questions so in this case atm.…read more

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