Kinetic Theory and Respiration
The kinetic atomic theory of gases has no sensible explanation for the gas exchange processes involved in human, and other mammalian, respiration.
This exchange is the absorption of oxygen into, and the emission of carbon dioxide from, the blood.
The effective parts of human lungs are hundreds of millions of minuscule air sacs, alveoli, and these balloon like sacs are composed of a structural membrane infused with blood vessels, the internal surfaces of these membranes that are in contact with atmospheric gases are covered with a liquid surfactant.
In six adult human lungs, the mean alveolar number was 480 million (range: 274–790 million; coefficient of variation: 37%). Alveolar number was closely related to total lung volume, with larger lungs having considerably more alveoli. The mean size of a single alveolus was rather constant with 4.2 × 106μm3 (range: 3.3–4.8 × 106μm3; coefficient of variation: 10%), irrespective of the lung size. One cubic millimeter lung parenchyma would then contain around 170 alveoli.
https://www.atsjournals.org/doi/full/10.1164/rccm.200308-1107OC
In the process of mammalian respiration the muscular expansion of the rib cage results in a reduction in pressure in the lungs, a consequent inhalation of atmospheric gases and the expansion of alveolar sacs and accordingly the introduction of nitrogen and oxygen into these sacs.
The proportions of nitrogen and oxygen in the atmosphere are, if we exclude the tiny proportions of other gases, around 80% and 20% respectively.
For humans the period between the commencement of inhalation to the completion of exhalation is, dependent upon the rate of physical exertion, normally between 1 second up to 4 seconds.
Of the 20% proportion of oxygen available in the atmosphere, it is observed that only 25 to 30% of this is actually absorbed by the lungs in each cycle, or in other words around 6% of the total of gases inhaled.
Even at a high level of exertion, with a inhalation to exhalation rate of around one second, oxygen is absorbed into the blood within the alveoli.
In essence the process of respiration is that the oxygen inhaled passes through the surfactant and the alveolar membranes and is absorbed into the blood vessels, while carbon dioxide gas is coincidentally expelled by them and passes in the opposite direction into the gas contained within the sac.
And so the gas exhaled is composed of around 80% nitrogen, 19-24% oxygen and the balance is carbon dioxide.
But it is an observed fact that the diffusion of gases is a slow process, and if we apply this to the atmospheric gases in the alveoli and, for the sake of argument, say there are many millions of atoms/molecules in one sac, this would suggest that the molecules of oxygen that are some distance away from the internal surface would not come into contact with it.
In the limited time allowed of one second, it is quite clear that statistically speaking it would be impossible for 25-30% of the oxygen atoms to collide with the surface.
However this is not the only problem for the kinetic atomic theory of gases in these circumstances.
The theory states that the di-atomic molecules of nitrogen and oxygen in the atmosphere are enclosed in a vacuum, or non-material ’empty space’ of a volume 1000 times that of the total volume of all the component atoms.
These molecules are in free ‘kinetic’ motion in this ‘space’ at average velocities of between 400 and 500 metres per second.
The AMU (atomic mass units) of nitrogen and oxygen di-atomic molecules are quite close, at about 14 and 16 respectively.
In such circumstances we can state that these molecules of nitrogen and oxygen, having similar atomic masses, are colliding with the atoms at the surface of the surfactant, and are traveling at similar (and often the same) high velocities.
And the theory suggests that such collisions are to be assumed as instantaneous.
The diagram below represents this ‘kinetic’ situation with the appropriate proportions of each element.
For the observed proportion of the available oxygen to enter the blood, and bearing in mind that absorption of nitrogen into the blood is dangerous and normally does not occur, it would require that each and every instantaneous ‘kinetic’ collision of an oxygen atom/molecule would result in absorption, while each and every instantaneous collision of a nitrogen atom/molecule would result in an immediate repulsion at the surface of the surfactant fluid.
That the internal surfaces of the alveoli have the capability of sensing the difference instantaneously between the atoms/molecules of oxygen and nitrogen in collisions and absorbing one while repulsing the other, is inconceivable.
There is clearly no answer to this question in terms of a kinetic atomic theory of gases and, if looked at objectively, this effectively falsifies the theory.