Fundamentals of Physics 5b)
Falsification of Kinetic Theory
Phase Changes
The Ideal (Perfect) Gas Laws are another example and are an imperfect model of the reactions of gases to changes in pressure and temperature, and even then in a limited range of conditions. Even with numerous subsequent modifications and adjustments they still fail to produce a model which can be relied on today.
For example a textbook states that ‘ The ideal-gas equation is not valid at high pressures’ and ‘the ideal gas equation is valid for all gases at sufficiently low densities and sufficiently high temperatures’.
A clear example is that these laws completely fail to predict the behaviour of gases during the change of state from gas to liquid. An example is Carbon Dioxide at the point of liquidisation. Another textbook quote ‘for carbon dioxide at 60 ATM all similarity to perfect gas behaviour is lost’.
Let us look at this particular change of state more closely. According to Kinetic Theory the progression from gas to liquid should follow the progression as shown in the graph below for a ‘Perfect Gas’ and this is valid initially. Which means that in Kinetic Theory terms the molecules, being confined into less and less ‘space’ due to the increase in applied pressure, collide more and more often with the walls and each other thus generating an increasing resistance to the applied pressure.
According to Kinetic Theory atoms in a gas at Standard Temperature and Pressure are positioned in relation to each other at 10 molecular diameters and in a liquid at less than one molecular diameter apart.
The progression in the graph above shows that at a point where the molecules are on average about 4 diameters apart there is suddenly no additional resistance to the applied pressure and the molecules essentially move to 1 diameter apart and the gas liquefies.
Current teaching of Kinetic Theory principles attempts to explain this anomaly by saying that at Standard Temperature and Pressure separations there is no attraction between the molecules of a gas and that as the separation reduces progressively they begin to attract and the attraction increases strongly at around 4 diameters and then, in the liquid state at 1 diameter, the force between molecules then reverses and becomes strongly repulsive.
This explanation is illogical. How can there, at one point in the progression, be no attraction, then attraction increases and then decreases to a point where there is neither attraction or repulsion, then finally strong repulsion develops?
What are these attractive and repulsive forces and what is causing them to vary in an irregular fashion? How do they act through and in a vacuum?
There is no rational explanation for these changes from attraction to repulsion.
This pattern follows the whole development of Kinetic Theory from Clerk Maxwell’s Laws to the present day, in that where natural phenomena or experimental results have not conformed to the theory then ad hoc ‘adjustments’ have been made one after the other in order to try and tailor the theory to suit the observed phenomena. This leaves us today with a theory which is so convoluted and ‘adjusted’ so that even where it is capable of practical application is extremely complicated and cumbersome. It needs to be reiterated that it is of course a ‘theory’ which means that there is no experimental evidence which unequivocally proves that molecules are moving a high velocities in a vacuum in any gas. Any contrived experiment that has been carried out to prove this theory have been on the basis of assumptions whereas the examples above are naturally occurring phenomena.
Richard Feynman states in The Feynman Lectures in Physics 5, Kinetic Theory :-
“It is obvious that this is a difficult subject, and we emphasize at the beginning that it is in fact an extremely difficult subject, and that we have to deal with it differently than we have dealt with the other subjects so far. In the case of mechanics and in the case of light, we were able to begin with a precise statement of some laws, like Newton’s laws, or the formula for the field produced by an accelerating charge, from which a whole host of phenomena could be essentially understood, and which would produce a basis for our understanding of mechanics and of light from that time on. – but we do not learn different physics, we only learn better methods of mathematical analysis to deal with the situation.
We cannot use this approach effectively in studying the properties of matter. We can discuss matter only in a most elementary way; it is much too complicated a subject to analyze directly from its specific basic laws, which are none other than the laws of mechanics and electricity. But these are a bit too far away from the properties we wish to study; it takes too many steps to get from Newton’s laws to the properties of matter, and these steps are, in themselves, fairly complicated. We will now start to take some of these steps, but while many of our analyses will be quite accurate, they will eventually get less and less accurate. We will have only a rough understanding of the properties of matter.”
(Note the emphasis ‘extremely‘ is Feynman’s own, the others are mine)