Introduction internal energy, change

Although the enthalpy and internal energy of a sample may have similar values, the introduction of the enthalpy has very important consequences in thermodynamics. First, notice that because H is defined in terms of state functions (U, p, and V), the enthalpy is a state function. The implication is that the change in enthalpy, H, when a system changes from one state to another is independent of... 

The removal of a partition or the introduction of a catalyst is the lifting of a restraint. They may result in either of the two possibilities either the system stays as it was, with the same value of or it undergoes an internal change, such as the fiow of energy or of matter, or a chemical reaction. This is equivalent to an increase in 11, the number of quantum states which the system can take up, each of... 

In the simple introduction above, the cross section in Eqn. (10.13) represents elastic scattering, for which the internal states of the particles do not change, and their relative kinetic energy E is the same before and... 

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