GEORGE A. LINHART 249 



under the direction of Lewis.^ However, the compounds in whose 

 entropy Lewis and his coworkers are at present interested are not of 

 the type which suit our purpose. Furthermore, it may take many 

 years before the data which we desire become available. We have, 

 therefore, decided to set up a specific heat apparatus of our own, as 

 well as a high precision bomb calorimeter outfit, for the accurate 

 measurements of heats of combustion of carbohydrates and other 

 organic compounds directly connected with our work. In the mean- 

 time, we are conducting experiments with nitogen fixation bacteria 

 to determine the most favorable conditions for the obtaining of inter- 

 pretable data. 



It may be of interest to show just how the free energy calculations 

 of a biological process are made from approximate data found in the 

 literature. 



If we wish to find the efficiency of the process of the fixation of 

 nitrogen by Azotohacter in a 0.1 molal solution of mannite, it is only 

 necessary to consider the mannite in the thermodynamic calculations, 

 since the concentration of the essential salts added is extremely 

 small compared with that of the mannite itself. 



{a) Calculation of AH for the Reaction. — 



6C + 14H + 60 = CbHmOs 



This is equivalent to the heats of formation of 6 mols of 002 plus 

 7 mols of H2O minus that of the reaction 



CaHuOfi + 6| O2 = 6 CO2 + 7 H2O 



or 



AH = 6(-94,2S0) + 7(-68,280) - (-728,400) = -315,060 calories 



(b) Calculation of TAS for the Same Reaction. — In order to calculate 

 the entropies of the substances involved in the above reaction, we 

 must know their specific heats from the absolute zero up to 25°C., 

 the temperature at which the reactions take place. The entropy of 

 each substance is related to the average atomic heat at constant 

 volume, Cp, by the thermodynamic equation: 



S = 



CvdlnT = 2.3 I Cvd log T (2) 



Jo 



^ The measurements are being made in the chemical laboratory of the Univer- 

 sity of California under the direction of Dr. G. N. Lewis. 



