The Chemistry of Gases

Air also contains other constituents, the abundances of which are quite variable in the atmosphere. Examples are water (H2O), 0-0.07 ozone (O3), 0-7 X 10 carbon monoxide (CO), 0-2 X 10 nitrogen dioxide (NO2), 0-2 x 10 and sulfur dioxide (SO2), 0-1 X 10 . 

UNIT III Kinetic Molecular Description of the States of Matter 

Carbon dioxide, CO2, is dissolved in aqueous solution to form carbonated beverages. Carbon dioxide also reacts with water to produce H2C03(a(7), which provides some of the acidity in soft drinks. Solid carbon dioxide (dry ice) is used for refrigeration. 

Sulfur dioxide, SO2, is produced by burning sulfur in air as the first step in the production of sulfuric acid. 

Sulfur trioxide, SO3, is a corrosive gas produced by the further oxidation of sulfur dioxide. 

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Of all the well-known revolutions in the history of science, the chemical is perhaps the most dramatic. The rapidity with which Lavoisier s views superceded those of the phlogistic tradition of the previous century is in contrast with the century and a half between Copernicus and Newton that defines the scientific revolution. Only twenty years separate Lavoisier s first explorations of the chemistry of gases and the public capitulation of... 

It was the development of the chemistry of gases that contributed chiefly to the overthrow of the theory of phlogiston. Yet the men whose discoveries contributed most definitely to that end were all themselves plilogistonists, with the single exception of Lavoisier, who was himself less a discoverer than a clear interpreter of the results of others. 

The researches which distinguish Black, Cavendish, and Priestley as chemists, were almost entirely on the preparation, properties, and reactions of gases. On account of the importance of the chemistry of gases or pneumatic chemistry in the development of chemical science, it will be worth while to follow chronologically the work and ideas of chemists on this subject, the researches and views of Van Hclmont, Rey, Boyle, Hook, and Mayow having already been considered. 

David Macbride, a prominent surgeon of Dublin, was the next to contribute to the chemistry of gases. He published a work entitled Experimental Essays in 1764. Macbride was especially interested in the fermentation processes in the animal body. Knowing that fixed air was an important product of these fermentations, he was led to investigate fixed air. His book consists of five essays, two of which, On the nature and properties of fixed air, and On the dissolvent power of quicklime, contain his contribution to the knowledge of fixed air. 

The methods of fractional liquefaction and distillation have very many similar and important applications in the chemistry of gases. 

He elucidated the role of oxygen in combustion and respiration and gave the substance that name. He fully incorporated the chemistry of gases into chemical science. 

It is true that Black did little himself to develop the consequences of the chemistry of heat for the chemistry of gases and of other substances. But that does not mean that for him heat was a physical externality to chemical process. On the contrary, as Golinski puts it ... 

Incidentally, you might think that because different gases have different size particles the volume of samples with the same number of particles would be different. It turns out, though, that the particles of a gas are so far apart that the size of the particles is negligible compared with the overall volume of the gas. In other words, at equal temperatures, equal numbers of particles of a gas occupy equal volumes. Or to put it another way, 1 cm of any gas at room temperature and pressure will contain about 25000000000000000000 particles. Equal volumes of gases at the same temperature and pressure contain the same number of particles . This means that you don t have to count the particles when considering the chemistry of gases ... 

Here are some examples of propositions presented explicitly as laws. John Dalton (1766-1844) proposed his Law of Partial Pressures as an important bridge between the physics and the chemistry of gases. He expressed the law as follows When any two or more gases acquire an equilibrium, the elastic energy of each against the surface of the vessel or any liquid, is precisely the same as if it were the only gas present occupying the whole space and all the rest were withdrawn . Dalton thought the law reflected not only the atomicity of matter, but also the uniformity of the distinct atoms of each chemical substance. Each component gas... 

This is not new. Consider Dalton s Law of Partial Pressures. This law has to do with the behaviour of molecular ( atomic for Dalton) constituents of a mixture of gases. This law is as much part of physics as Boyle s Law. Of course, it places some constraints on the range of possibilities of reactions that are the proper topics of the chemistry of gases. 

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