Energy from fuels

Some average bond energies are shown in Table 12.1. This is the heat energy or enthalpy that is required to break one mole of the bond in question. Since bond cleavage and bond formation are the reverse of each other, this is also the heat energy that is released upon formation of one mole of the 

The energy changes associated with chemical reactions fall into three different categories  

One can, in principle, calculate the heat energy (enthalpy) change in a chemical reaction if the balanced chemical equation is known and the bond energies of all the bonds broken and made are known. For our purposes, we have only included a very abbreviated table (Table 12.1) of the types of bonds that might be involved in the combustion of a hydrocarbon or related fuel. 

Heat of combustion The quantity of heat released when a fuel is burned variously expressed as kcal/mol, kcal/g, kJ/mol, or kJ/g 

Octane and 2,2,4-trimethylpentane (both of which have the same formula, GgHjg, a molecular weight of 114 g/mol) release the same amount of energy ( — 5,049 kJ/ mol or 44.3 y/g) upon combustion. Both reactions, shown below, involve the breaking and formation of exactly the same types and numbers of bonds. Note in the analysis below that the balanced 

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Alcohol dehydrogenases found in certain microorganisms utilize a pyrroloquino-line quinone (PQQ) or flavin cofactor to pass electrons released upon oxidation of alcohols to the heme electron-acceptor protein, cytochrome c. These membrane-associated alcohol dehydrogenases form part of a respiratory chain, and the energy from fuel oxidation therefore contributes to generation of a proton gradient across... 

Industnal solid wastes -energy from [FUELS FROM BIOMASS] (Vol 12)... 

These oxidation reactions employing pyridine nucleotides and flavoproteins are especially important in primary metabolism in liberating energy from fuel molecules in the form of ATP. The reduced coenzymes formed in the process are normally reoxidized via the electron transport chain... 

Figure 14.12. Stages of Catabolism. The extraction of energy from fuels can be divided into three stages.

VVe can divide metabolic pathways into two broad classes (1) those that convert energy from fuels into biologically useful forms and (2) those that require inputs of energy to proceed. Although this division is often imprecise. it is nonetheless a useful distinction in an examination of metabolism. Those reactions that transform fuels into cellular energy are called catabolic reactions or, more generally, catabolism. 

Distinguish between the reactions that cells use in the presence and in the absence of oxygen to extract energy from fuel molecules. Explain how a small number of biochemical building blocks can be used to make the extraordinary variety of molecules needed to perform life s chemical functions. 

Today, a significant portion of the fuel burned in an ICE vehicle is used to generate electrical energy for the various on-board electric components (about 11 per 100 km, and even more in high-end cars) [31]. Inefficiency in the conversion of energy from fuel to electricity, some of which may be stored in the battery for a time, increases fuel consumption by about 0.151 per 100 km to support a 100-W load, for example... 

Figure 9.18 Bond strength and the energy from fuels. Fuels with weaker bonds release more energy during combustion than do fuels with stronger bonds.

Energy from fuel oxidation is converted to the high-energy phosphate bonds of adenosine triphosphate (ATP) by the process of oxidative phosphorylation. Most of the energy from oxidation of fuels in the TCA cycle and other pathways is conserved in the form of the reduced electron-accepting coenzymes, NADH and FAD(2H). The electron transport chain oxidizes NADH and FAD(2H), and donates the electrons to O2, which is reduced to H2O (Fig. 21.1). Energy from reduction 0/O2 is used for phosphorylation of adenosine diphosphate (ADP) to ATP by ATP synthase (FgFjATPase). The net yield of oxidative phosphorylation is approximately 2.5 moles of ATP per mole of NADH oxidized, or 1.5 moles of ATP per mole of FAD(2H) oxidized. 

Extracting Energy from Fuel Molecules Oxidation... 

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