206 MAX KLEIBER 



one to predict the direction a chemical process is likely to take. 

 The "driving force" of a chemical reaction (11) is measured by the 

 decrease in free energy. A given increase in free energy indicates for 

 a given process how much work, or electrical or radiant energy, is at 

 least necessary to make the process take place. The knowledge of 

 free energy, however, does not permit the prediction of the work ac- 

 tually required to produce a given reaction, or the work that can 

 actually be gained from a reaction. The free energy also does not 

 predict the rate at which a given reaction will proceed. The fact 

 that glucose has a heat of combustion of 673 kcal. per mole tells us 

 only that so much heat is developed ivhen 1 mole of glucose combines 

 with oxygen to form carbon dioxide and water. It does not tell us 

 whether in a mixture of glucose, carbon dioxide, and water, more glu- 

 cose and oxygen will be found after a given time with heat absorption, 

 or more carbon dioxide and water with heat production. 



That the combustion of glucose is accompanied by a decrease of 

 free energy of 688 kcal. indicates a "driving force" in the direction of 

 oxidation rather than synthesis of glucose. This knowledge, how- 

 ever, does not enable us to predict whether or not, in a given mixture 

 of glucose, oxygen, carbon dioxide, and water, combustion at a meas- 

 ureable rate will take place at all. That question involves the kinet- 

 ics of catalytic processes, especially enzyme reactions, and is beyond 

 the limits of calorimetry and even thermodynamics. 



E. ACCOMPLISHMENT OF CALORIMETRY 

 AND OUTLOOK 



1. Practical Importance of Heat Transfer 



Heat transfer is so universal that hardly any branch of modern 

 industry could function without the great amount of knowledge on 

 thermal processes that has accumulated during the last two centuries. 

 The importance of calorimetry goes even beyond factories and ma- 

 chines. The planning of houses and clothing, the methods of build- 

 ing dams and bridges are among the activities that depend on calori- 

 metric data, many of them available in handbooks. The use of such 

 data would be simplified if the engineers among the English-speaking 

 peoples were to follow the example of the engineers of the rest of the 

 world in regarding engineering as applied physics. This attitude 

 w^ould lead to a unified terminology in all modern calorimetric and 



