226 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



it was not until 1851 that Lord Kelvin and Clausius combined it with 

 the first law to produce the present science of thermodynamics, in its 

 application to physical phenomena. Then, in the period between 

 1873 and 1878, Willard Gibbs published his great papers dealing 

 with the application of thermodynamics to chemical phenomena. 

 Gibbs' work put the science of chemical thermodynamics in nearly 

 its final form ; only one more great discovery remained to be made — 

 that of the third law of thermodynamics, by W. Nernst at the begin- 

 ning of the twentieth century. 



Let us contrast the knowledge about a chemical reaction available 

 in 1847 with that in 1947. In 1847 a reaction involving the conversion 

 of certain reactant substances into certain products, such as nitrogen 

 and hydrogen into ammonia, could be discussed only to the extent that 

 direct experimental information, obtained by observing the reaction 

 itself, was at hand. Only if the reactants had actually been observed 

 to combine to form the products could the process be said to be a pos- 

 sible chemical reaction. The amount of heat evolved or absorbed 

 during the reaction would have been known only if the reaction had 

 actually taken place, and the heat evolution or absorption had been 

 measured. The question of increasing the yield of the product could 

 not have been discussed at all, for there was no knowledge as to whether 

 increasing the temperature, increasing the pressure, or making other 

 changes in the system would increase or decrease the amount of product 

 obtained. In 1947 it was possible, from knowledge of the thermody- 

 namic properties of the reactant substances and the products, to pre- 

 dict, for a reaction that has never been observed to occur, most of its 

 important characteristics — the amount of heat that would be evolved 

 or absorbed when the reaction takes place, and the extent to which it 

 would take place, in its dependence on temperature, pressure, con- 

 centrations of the reactants, and other factors. There still remains, 

 however, one most important question to which a definite answer can- 

 not in general be given. This is the question as to the rate at which the 

 reaction will take place under given circumstances. We are not yet 

 able to make predictions about this rate of reaction, except for certain 

 simple systems. The field of chemical thermodynamics is in nearly its 

 final state of development ; the field of chemical kinetics is just begin- 

 ning to be developed. 



Chemical thermodynamics, like nearly every other field of chem- 

 istry, has been influenced by the great progress that has taken place 

 in the extension of our knowledge of atomic and molecular structure 

 during the past few decades. The electron itself was discovered in 

 1897, and the atomic nucleus in 1911; since then a penetrating and 

 detailed understanding of the electronic and atomic structure of 

 matter has been obtained, and chemists are now able to talk about the 



