Gases
Gases, like other kinds of matter (solids , liquids and plasma), are formed of molecules or atoms. In the cases of gases these molecules and/or atoms move around and bounce of the walls of the container, as it is shown on the animation below, which depicts a gas inside a container. Try the temperature control on the left, to see what changes>>
An increase in temperature correspond to an increase in the speed of the atoms (as seen on the animation above); this will also cause more frequent collisions with the walls and consequently, an increase in pressure. If you increase the number of atoms the pressure will also increase (that is easier to visualise, isn't it?)
Pressure, which is a macroscopical effect, is caused by electrons hitting the walls of the container ( a microscopic effect). Obviously, an increase on the number of particles (N on the equation on the left) will also cause an increase in pressure.
Temperature is also a macroscopic measurement. Isolated atoms or molecules don't have a temperature.
If the number of particles is kept constant, that ideal gas equation simplifies to:
PV = T
The behaviour of each particle on the gas can be modeled using Newtons equations, spo that the ideal gas equation shown above can be deduced by first principles (that is called kinetic theory of gases).
Gases may be atomic or molecular.A common example of an atomic gas is Helium; all inert gases (located at the last column of the periodic table on the right) are atomic gases. In this case each particle of the gas is only an atom (isolated).
Gases like Oxygen or Nitrogen (which form the terrestrial atmosphere) are molecular. Two oxygen atoms form the oxygen molecule and two nitrogen atoms form the nitrogem molecule (gas molecules may also be composed of more than two atoms).
Each atom (or molecule) in the gas can move freely. A gas will occupy all the volume available to it; as the size of the container increases, the pressure of the gas diminishes.
In animation 1, above, we see a gas inside a container which is smaller than the one in
animation 2 (below).
As a result, the atoms collide much more often with the walls of the container; this fact is perceived macroscopically as an increase in pressure (the atoms moving and colliding constitute the microscopical view).
The animations just show 3 atoms in the container but in a normal situation
you will have many billions of them and they will be very small .