Net energy release

Note that when q" = 0, 7b is the adiabatic flame temperature. We can regard this equation as a balance between the net energy released and energy lost ... 

In this case, the loss is considered solely to the duct wall at 25 °C. The net energy release is computed as above (Equation (4.43)) and the loss to the wall per unit duct cross-sectional area is... 

In the high-pressure limit conditions considered in this section, association reactions are, in principle, the reverse of the fission reactions discussed previously. That is, although the association process initially results in the formation of a chemically activated adduct—as a consequence of net energy released by the exothermic association process—this energy is... 

Where does the net energy released in an exothermic reaction go ... 

Tile first iwo equations represent tlie fact that the D-D reaction can follow either of Iwo paths, producing tritium and one proton or helium-3 and one neutron, wirli equal probability. The products of the first two reactions form the fuel for the third and fourth reactions, and they are burned with additional deuterium. The net reaction consists of the conversion of six deuterium nuclei into two helium nuclei, two hydrogen nuclei, and two neutrons along with a net energy release of 43.1 MeV. The reaciion products—helium, hydrogen, and neutrons—are harmless as... 

Just as an ordinary chemical equation is a shortened version of the complete thermochemical equation which expresses both energy and mass balance, each nuclear equation has a term (written or implied) expressing energy balance. The symbol Q is usually used to designate the net energy released when all reactant and product particles of matter are at zero velocity. Q is the energy equivalent of the mass decrease (discussed above) accompanying the reaction. Q is usually expressed in MeV. 

The initiation of this process requires 3 + 16 = 19 kcal/mole, but there is a net energy release of AE = -31 kcal per mole of 18B. 

It should be pointed out that the mechanism by which the reaction occurs is much more complicated than Eq. 15.8-1 implies. Many intermediate compounds, and also enzymes acting as biological catalysts, are involved. The precise mechanism of this reaction is discussed in basic biology courses. However, as the sum of all the reactions is as shown in Eq. 15.8-1, from the point of view of thermodynamics, that is the only reaction we need to consider if our interest is solely in the net energy release (Sec. 

Exergonic A chemical process in which there is a net energy release. 

Excited state An unstable, higher energy state of an atom Exergonic A chemical process in which there is a net energy release... 

Usually, the quenching of an excited electronic state leads to a strong multiquantum vibrational excitation of a molecule. Sometimes, however, the electronic transition is accompanied by a one- or two-quantum vibrational transition with very small net energy release. This is the case when the electronic initial and final states are the fine-structure terms of a heavy atom. One of such processes... 

Combustion of methane requires breaking of 4 X C-H bonds and 2x0 = 0 bonds (+2640 kJ moH), but makes 2 X C = O bonds plus 4 X O-H bonds (-3332 y moH), giving a net energy release of-692 kJ mol" (This is an approximation to the accurate value of 890 kJ mob because we used average bond energies rather than the specibc values for the molecules involved.)... 

The facilitating action of enzymes is due to their ability to direct the S - P reaction in such a way as to meet a lower energy barrier. Thus, the probability of the enzymatic reaction is greater than the probability of the spontaneous one. This is shown in Figure 16b. Enzyme-substrate binding, enzyme-product formation and product release are separated from each other by energy barriers and tranaent states, but the barriers are lower and so the reaction is easier with than without the enzyme. The net energy released in 5 - P remains the same. 

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