LAWS OF THERMODYNAMICS 163 



Specify Heat (c) — the heat energy required to raise 1 g of a substance one 

 degree in temperature. A particularly important specific heat is that of 

 water, by which the unit of heat energy is defined: One calorie is the amount 

 of heat energy required to raise 1 g of pure water 1°C, from 3.5 to 4.5°C 

 (where it is the most dense) at 1 atm pressure. 



Heat Capacity {(.') — the heat energy required to raise 1 molecular vvt of 

 substance 1 deg in temperature. The units of specific heat, c, are cal/deg 

 Cent, g; and of heat capacity, C, are cal/deg Cent. mole. 



Other forms of energy to be discussed are mechanical, electrical, gravita- 

 tional, chemical, nuclear, etc. Energetics or thermodynamics is the study 

 of interconversion of these. In biological systems the subject is usefully- 

 called bioenergetics. That part of the subject dealing with electromagnetic 

 and matter waves was considered in Chapters 3 and 4, and is expanded in 

 Chapter 9. 



LAWS OF THERMODYNAMICS 



Statements of the Three Laws 



There are three general principles which summarize human experience 

 with energy interconversion. They are negative laws in the sense that they 

 cannot be proved always to hold, but nevertheless never have been known 

 to be violated. 



The First Law: The first law states simply that energy can be transformed 

 from one form to another but cannot be created or destroyed. After the 

 equivalence of matter and energy were recognized (and proved in nuclear 

 reactions), the law was generalized still further to read: "mass-energy" in- 

 stead of "energy." 



The Law stands as written, needing no extension, for all cases in which 

 any form of energy is converted into heat: 100 per cent conversion can al- 

 ways be realized. In Figure 7-1 (b) each of the arrows originates in a form 

 of energy other than heat. 



The Second Law: For any machine which converts heat into mechanical 

 work, chemical into electrical energy, or the like, it is a universal experience 

 that only a fraction can be converted; the rest remains unavailable and un- 

 converted. There is thus an amount of unavailable energy as well as available 

 energy from the conversion. The unavailable, it would be logical to assume, is 

 the heat energy which must remain in the molecules of which the final state 

 (i.e., the product) is composed. 



The Third Law: At 0°K (-273.16°C), the absolute zero of temperature, 

 at which all molecular motion has ceased, matter should be in a state of 

 perfect order, the molecules being perfectly aligned or oriented, and per- 

 fectly quiet. This law is concerned with the absolute heat energy contained 

 in molecules at any temperature. Although our present interest is in changes 



