Internal energy of reactants

All the above problems (effect of internal energy of reactants, product energy distribution, and determination of Cj) have been treated by Wolf [54] based on the phase space theory developed by Light [55]. 

The model also implies that the reaction cannot be endothermic. As will be discussed below, however, it has recently been shown that some endothermic reactions occur at the expense of internal energy of reactants or, at higher velocities, at the expense of ion kinetic energy. 

Even for molecules in the ground electronic state, our knowledge about cross sections is largely limited to the room-temperature condition, in which vibrational and rotational states are populated in a thermal distribution. Then, for a diatomic molecule, the ground vibrational state is predominantly populated. However, for a polyatomic molecule, normal modes with small quanta must be appreciably excited. For the full understanding of kinetics in plasma chemistry, it is important to assess the role of the internal energy of reactant molecules. 

Similarly, the internal energy of combustion is given as the difference in internal energy of the products and the internal energy of reactants... 

Ion/neutral reaction. Interaction of a charged species with a neutral reactant to produce either chemically different species or changes in the internal energy of one or both of the reactants. 

Thus, we see that overall rate constant that is determined from traditional bulk kinetics experiments for an elementary reaction is an average of microscopic observables, which are dependent on internal states of the reactants and products, the relative translational energy of reactants and the product scattering angle. Their relation may be summarised as follows ... 

Chemists define the total internal energy of a substance at a constant pressure as its enthalpy, H. Chemists do not work with the absolute enthalpy of the reactants and products in a physical or chemical process. Instead, they study the enthalpy change, AH, that accompanies a process. That is, they study the relative enthalpy of the reactants and products in a system. This is like saying that the distance between your home and your school is 2 km. You do not usually talk about the absolute position of your home and school in terms of their latitude, longitude, and elevation. You talk about their relative position, in relation to each other. 

In case of an intended protonation under the conditions of Cl one has to compare the PAs of the neutral analyte M with that of the complementary base B of the proton-donating reactant ion [BH]" (Brpnsted acid). Protonation will occur as long as the process is exothermic, i.e., if PA(b) < PA(m). The heat of reaction has basically to be distributed among the degrees of freedom of the [Mh-H]" analyte ion. [12,21] This means in turn, that the minimum internal energy of the [Mh-H]" ions is determined by ... 

All such reactions are characterized by a lowering of the cross section as the internal energy of the adduct is increased. The lifetime of the benzene dimer ion, as well as those of similar adduct ions, is very sensitive to its internal energy since it is very loosely bound (it has a binding energy of 8 kcal/mole). Increasing the product-ion internal energy by vibrational excitation of the reactant readily promotes the dissociation back into reactants. 

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