LAWS OF THERMODYNAMICS 171 



AF = -7.73 kcal/mole; AH = -4.8 kcal/mole. and AS = 0.45 cal/deg 

 mole. If the reaction occurs in a test tube, no energy is converted into useful 

 work, and the heat produced is 4.8 kcal/mole. If, however, it is carried out 

 in the presence of an activated actomyosin filament (the contractile unit in 

 muscle), mechanical work (lifting a weight, for example) can be made to 

 occur, and the amount of work done can be anything up to 7.73 kcal/mole, 

 depending upon how it is done. If done reversibly (infinitely slowly), 7.73 

 kcal/mole is done, and S = 100 per cent; if done more and more rapidly, 

 8 becomes less and less. 



The Production of Entropic Heat 



Note that S is a state variable, like F, H, and U, and note that AS may 

 be positive or negative depending on whether the heat capacity of the prod- 

 ucts is greater or less than that of the reactants. Note further that if AS is 

 negative, and it often is, AF will be greater than AH. This is really not 

 surprising if one remembers that the extra energy for work was bound up as 

 extra heat energy of the reactants. Note also that the greater the number 

 of rotations, vibrations, and translations of which a system is capable, the 

 greater the heat capacity and hence the greater the entropy. Therefore 

 entropy (a heat capacity) is often used as a measure of disorder: the greater the 

 entropy, the greater the disorder. 



For the living system, we write 



A3C = AJ + TAS 



under reversible conditions, and 



AJC = A3 7 ' + q' + TAS 



for practical conditions, in which not the maximum work, A{F, but rather a 

 lesser amount, Aj', is realized. An amount of energy, q', shows up as heat 

 energy and adds to the reversible, unavailable heat energy, TA S kcal. Of 

 course q' itself will factor into 7~A&', since it is a heat energy. Then if A S is 

 the reversible entropy increase, AS' is the extra entropy increase because 

 of the irreversibility of the process. Although q' is, strictly speaking, a waste, 

 it is the heat energy which maintains the temperature of a man some 10 or 

 more degrees C above his environment in spite of a steady heat energy loss 

 to the environment. Now, the work done may be internal work, A$' inV or 

 external work, A5 7 '- The internal work, however, is degraded into heat 

 internally, and forms part of q'. (Consider the pumping work of the heart, 

 for example: blood is forced along the circulatory system against a frictional 

 resistance, and the energy is finally expended as heat in the vessel walls.) II 

 we exclude growth and mental work for the moment (these hopelessly 

 complicate the argument), the contribution made by internal work to the 



