Conservation of Energy in Nuclear Reactions

Just as the partial derivative (pU/dT)y has the physical meaning of being the heat capacity at constant volume NCv, the other derivatives, called thermal coefficients, can be related to experimentally measurable quantities. The derivative rr,v = U/d )y j for example has the physical meaning of being the amount of heat evolved per unit change in the extent of reaction (one equivalent of reaction) at constant V and T. If rjy is negative the reaction is exothermic if it is positive the reaction is endothermic. Just as we derived the relation (2.3.6) between the heat capacities Cp and Cy, one can derive several interesting relations between these thermal coefficients as a consequence of the. First Law [16]. 

since the extent of reaction is a state variable, the enthalpy of a reacting system can be expressed as a function of the extent of reaction  

The heat of reaction per unit change of hpj, is the derivative of H with respect to 

At terrestrial temperatures, transformations of states of matter are mostly chemical, radioactivity being an exception. Just as molecules collide and react at terrestrial temperatures, at very high temperatures that exceed 10 K, typical of temperatures attained in the stars, nuclei collide and undergo nuclear reactions. At these temperatures, the electrons and nuclei of atoms are completely tom apart. Matter turns into a state that is unfamiliar to us and the transformations that occur are between nuclei, which is why they are called nuclear chemistry. 

All the elements heavier than hydrogen on our planet and on other planets are a result of nuclear reactions, generally known as nucleosynthesis, that occurred in the stars [17], Just as we have unstable molecules that dissociate into other more stable molecules, some of the nuclei that were synthesized in the stars are unstable and they disintegrate—they are the radioactive elements. The energy released by radioactive elements turns into heat it is a source of heat in the Earth. For example, the natural radioactivity in granite due to Th 

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