Understandings: Pressure, Differences between ideal and real gases, Mole, molar mass and the Avogadro constant
Guidance: Students should be aware of the assumptions that underpin the molecular kinetic theory of ideal gases. Students should understand that a real gas approximates to an ideal gas at conditions of low pressure, moderate temperature and low density
Utilization: Transport of gases in liquid form or at high pressures/densities is common practice across the globe. Behaviour of real gases under extreme conditions needs to be carefully considered in these situations.
Data booklet reference:
Pressure is the force acting on a surface divided by the area over which the surface is acting ( p = F/A). The units of pressure are newtons per square metre, which is given the special name pascals (symbol: Pa). Gases create pressure by the gas particles bouncing on the surfaces exposed to the gas. Atmospheric pressure is something we experience all the time but don't normally notice unless it increases or decreases significantly.
The calculation of gas pressure is dependent on the change of momentum of the particles as they impact the surface. Newton's second law allows to calculate the force required from this change in momentum, and Newton's third law shows how this force affects the surface.
An ideal gas is an approximation of a real gas. We use a set of assumptions (which are part of the Kinetic Theory of gases) to enable us to make calculations relating to real gases. An ideal gas is a good approximation for most gases in most situations, but doesn't work very well in extreme situations.
The assumptions of an ideal gas are that:
the gas consists of a large number of particles moving randomly
the particles are essentially zero volume, smooth and collide elastically
barring collisions, there are no forces acting on the particles
Ideal Gas laws break down when their assumptions are significantly violated. This includes very low temperatures, high densities and / or high pressures. In these circumstances gases will move towards or become liquids, in which the case the forces between particles becomes significant. The conditions in which a gas most closely approximates to an ideal gas is conditions of low pressure, moderate temperature and low density.
One property of a gas that we will need to deal with is the amount of a gas. This is normally expressed in moles (symbol: mol). One mole of a substance means that the number of particles of that substances is equal to Avogadro's Number (6.02214076×10²³).
One mole is therefore equal to the number of particles divided by Avogadro's number. To calculate the number of moles of a substance (n) we take the mass of the sample of substance you have (in grams) and divide by the molar mass, which can be found from the periodic table and the formula of the substance. For more information see the textbooks or here.
Oxford Physics: pp 102-109 this textbook mixes and matches with the Gas Laws, but is very good on how Newton's Laws support the mathematics of how gases behave.
Hamper HL (2014): pp 112 - 114
Pages 162 - 163 (last question is part of next section)