https://pubs.acs.org/doi/10.1021/acs.jchemed.5b00333# * ACS * ACS Publications * C&EN * CAS Find my institution Blank imageLog In logo Journal Logo Quick View Share Share on * Facebook * Twitter * WeChat * Linked In * Reddit * Email [ ] (*)J. Chem. Educ.( )All Publications/Website OR SEARCH CITATIONS [Journal of Chemical Education ] [ ][ ] My Activity Recently Viewed You have not visited any articles yet, Please visit some articles to see contents here. 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Chem. Educ. 2015, 92, 12, 2094-2099 Publication Date (Web):September 1, 2015 Publication History * Published online1 September 2015 * Published inissue 8 December 2015 https://doi.org/10.1021/acs.jchemed.5b00333 Copyright (c) 2015 The American Chemical Society and Division of Chemical Education, Inc. RIGHTS & PERMISSIONS Authors ChoiceACS AuthorChoice with CC-BY license Article Views 27193 Altmetric - Citations 28 LEARN ABOUT THESE METRICS Article Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days. Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView In * Add Full Text with Reference * Add Description ExportRIS * Citation * Citation and abstract * Citation and references * More Options Share on * Facebook * Twitter * WeChat * Linked In * Reddit * Email PDF (905 KB) Get e-Alerts Supporting Info (1)>>Supporting Information Supporting Information SUBJECTS: * Redox reactions, * Chemical reactions, * Fuels, * Molecules, * Enthalpy Go to Volume 92, Issue 12 Get e-Alerts Abstract [ed-2015-00] High Resolution Image Download MS PowerPoint Slide The strongly exothermic nature of reactions between molecular oxygen and all organic molecules as well as many other substances is explained in simple, general terms. The double bond in O[2] is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in CO[2] and H[2]O results in the release of energy, which is given off as heat or increases thermal motion. This explains why fire is hot regardless of fuel composition. The bond energies in the fuel play only a minor role; for example, the total bond energy of CH[4] is nearly the same as that of CO[2]. A careful analysis in terms of bond enthalpies, counting double bonds as two bonds to keep the total number of bonds unchanged, gives the heat of combustion close to -418 kJ/mol (i.e., -100 kcal/mol) for each mole of O[2], in good agreement (+-3.1%) with data for >500 organic compounds; the heat of condensation of H[2]O, -44 kJ/mol, is also included in the analysis. For 268 molecules with >= 8 carbon atoms, the standard deviation from the predicted value is even smaller, 2.1%. This enables an instant estimate of the heat of combustion simply from the elemental composition of the fuel, even for a complex mixture or unknown molecular structure, and explains principles of biofuels production. The analysis indicates that O[2], rather than fuels like octane, H[2], ethanol, or glucose, is the crucial "energy-rich" molecule; we briefly explain why O[2] is abundant in air despite its high enthalpy. KEYWORDS: * First-Year Undergraduate/General * Upper-Division Undergraduate * Physical Chemistry * Misconceptions/Discrepant Events * Thermodynamics * Textbooks/Reference Books * * * Introduction ARTICLE SECTIONS Jump To --------------------------------------------------------------------- Fire has fascinated humans since time immemorial, and it was one of the four Greek classical elements. In our daily lives, reactions of organic molecules with oxygen from the air are crucial to provide useful energy, via combustion in furnaces and heat engines, while in our bodies, the cellular respiration of O[2] is an indispensable energy source. Why these important reactions are always exothermic, or in lay terms, why fire is hot regardless of the fuel, is a fundamental chemistry question that should be explained in general- and physical-chemistry textbooks. Surprisingly, a simple, valid explanation of the exothermicity of combustion reactions has apparently not been provided,(1-5) not even in textbooks on combustion(6-9) or in the technical literature on heats of combustion.(10-12) While calculations of heats of combustion to four significant figures for specific combustions reactions, based on tabulated heats of formation, are part of most chemical thermodynamics courses,(1-5) they do not represent any insight since most tabulated heats of formation were in turn determined from measured heats of combustion, (10) which means that the reasoning is cyclical. Empirical multiparameter fits of experimental data to produce an equation predicting the heat of combustion (per gram) from the elemental composition(11, 12) also do not provide much understanding. We show below that a straightforward, general explanation of what makes fire hot can be provided in conceptual general-chemistry terms and results in a simple, predictive formula for heats of combustion. The heats of reaction of a few specific combustion reactions have been explained in terms of bond energies,(5, 7) but this has not revealed why all combustions of organic molecules are exothermic. Most bond-energy analyses have remained opaque since double bonds were treated on par with single bonds. We count double bonds as two bonds since the total number of electron-pair bonds is the same in reactants and products; only when the number of bonds remains unchanged is a general analysis per bond meaningful. On this basis, it becomes apparent that combustions are exothermic because of the unusually small bond-dissociation energy of O[2] (per pair of electron-pair bonds). This fact is not obvious in the conventional analyses. The energy of "the O-O bond" in O[2], 498 kJ/mol at 298 K, (13) is even somewhat larger than that of H-H (436 kJ/mol),(13) C-H (ca. 410 kJ/mol),(14-16) or C-C (ca. 350 kJ/mol)(16, 17) bonds, while the calculation in terms of enthalpies of formation(1-5) sets the enthalpy of O[2] to zero and thus completely hides the molecule's bond energy. An attempted explanation of the exothermicity of combustions in terms of changes in electronegativity differences of bonded atoms(3) does not stand up to closer scrutiny, as shown below. Our semiquantitative bond-energy analysis indicates, and a rigorous calculation confirms, that the heat of combustion is close to -418 kJ /mol for each mole of O[2] in the combustion reaction, most of which can be attributed to the relatively weak double bond of O[2]. We validate our result on >500 heats of combustion reported in the literature(10) and show that our simple formula predicts the heat of combustion accurately to a few percent for molecules without an excess of heteroatoms or for any larger molecules. As a timely application, we show how insights from this analysis can explain principles of biofuels production. Our analysis strongly suggests that O[2], rather than fuels like H[2], octane, ethanol, or glucose, is the crucial "energy-rich" molecule that makes combustion reactions highly exothermic. Finally, we briefly explain why in spite of its high bond enthalpy, O[2] is abundantly present in our atmosphere. Analysis and Discussion ARTICLE SECTIONS Jump To --------------------------------------------------------------------- Examples of Reactions Involving Fuels of "High Energy Density" The reactions of octane and ethanol with molecular oxygen[ed-2015-00] [ed-2015-00]are typical examples of strongly exothermic combustions, with heats of reaction exceeding 1 MJ/mol. (In general-chemistry textbooks, "/mol" is usually omitted;(16, 18, 19) see the discussion in the Supporting Information.) The concept of a "high energy density" of fuels such as H[2], octane, etc. might suggest that the chemical energy of combustion resides in these fuels. However, the reaction of solid carbon ("anthracite coal") and hydrogen ("rocket fuel")[ed-2015-00]is only weakly exothermic. However, when we add O [2] to these reactants,[ed-2015-00]the reaction is much more exothermic, which indicates that the underlying reason for the exothermicity of combustions must be sought with O[2], which we will confirm below. It is also instructive to consider[ed-2015-00]which is strongly exothermic without traditional fuels and without formation of CO[2] or H[2]O. This again underlines the crucial role of O[2], as does the comparison of the combustion[ed-2015-00]with the analogous, less exothermic reaction with H[2][ed-2015-00] The exothermic character of all combustions has occasionally been attributed to the formation of CO[2],(18) maybe based on its negative heat of formation (-393.5 kJ/mol) or its large C-O bond energy of 804 kJ/mol. This explanation is not valid since reactions producing CO[2] without O[2] as a reactant are not particularly exothermic (see the Supporting Information) and since the total bond energies of CO[2] and CH[4] (1608 and 1660 kJ/mol, respectively) are almost the same. Heat of Reaction in Terms of Bond Energies Combustions are exothermic if the products have a lower total enthalpy than the reactants. Reactants and products contain the same atoms, and only the bonding is different, so the heat of combustion, (3, 19) also known as the enthalpy (change) of combustion,(1) can be calculated from bond-dissociation energies D[i,m] and stoichiometric coefficients n[i] according to(5)[ed-2015-00](1) The sum over i in eq 1 includes all reactants and products, while the sum over m takes into account all bonds within reactant or product i. Note that in this bond-energy approach, the separated atoms (rather than the most stable forms of the elements(1-5)) define the zero point of the enthalpy scale. This zero point is shared by reactants and products since they contain the same atoms. Instead of the bond-dissociation energy, we will consider the closely related bond-formation enthalpy of bond m in substance i, per mole, which we define as[ed-2015-00](2) While bond-dissociation energies are more positive for stronger bonds, the enthalpy is reduced by bonding, so the bond-formation enthalpies used in the following are more negative for stronger bonds. Other details of bond energies and enthalpies are discussed in the Supporting Information. Most important in our analysis of combustion reactions are the total bond-formation enthalpies of O[2] (-498 kJ/mol), CO[2] [2 x (-804 kJ/ mol)], and H[2]O (-927 kJ/mol) at 298 K, which have been determined with high accuracy.(13) Enthalpies of C-H, C-C, C-O, and other bonds in the organic fuel(13, 17) are necessarily averages with greater uncertainties, but this does not significantly affect our analysis since the well-defined -306 kJ/mol difference between the double-bond enthalpies of O[2] and of C-O in CO[2] is dominant. Unchanged Number of Electron-Pair Bonds in Combustion Reactions Our analysis of the enthalpy per bond or pair of bonds will be based on the observation that the total number of bonds does not change during a combustion reaction if double bonds are counted as two bonds and triple bonds as three. Examples are shown in Figure SI1. To confirm this result more generally, we consider the main elements in organic fuels, where C usually has four electron-pair bonds, O has two bonds, and H one bond; this holds before and after the reaction. In this atom-based analysis, every bond is counted exactly twice, so the total number of bonds in reactants containing n[C] carbon, n[O] oxygen, and n[H] hydrogen atoms is given by[ed-2015-00](3) Since the numbers of C, O, and H atoms, n[C], n[O], and n[H], are the same in the reactants and products, according to eq 3, the total numbers of bonds in reactants and products are also the same. This applies even for special cases like C[?]O and ionic groups (see the Supporting Information). Bond Enthalpy Changes for Model Combustion Reactions According to eqs 1 and 2, we can estimate the heat of reaction in terms of bond-formation enthalpies. To provide some simple examples, Figure 1, panel a shows the enthalpies of a few molecules relevant in combustions in terms of four bonds. Specifically,[ed-2015-00] [ed-2015-00] Figure 1 [ed-2015-00] Figure 1. Bond-formation enthalpies of (a) four and (b) two moles of electron-pair bonds in reactants (left) and products (right) relevant for (a) combustion of hydrogen and of methane; (b) combustion of a general C-, H-, and O-containing organic fuel. Note that the bond-formation enthalpy of the double bond in O[2] is distinctly higher (less negative) than that of other pairs of bonds. High Resolution Image Download MS PowerPoint Slide There are eight bonds in the reactants and eight in the products, so if the average enthalpy per bond is higher in the reactants, the reaction is exothermic. More conveniently, an analysis of the enthalpy per four bonds shows that CH[4], CO[2], 4 H[2], and 2 H[2]O (four bonds each) have similar bond enthalpies, while the enthalpy of 2 O[2] is ~2 x 430 kJ/mol higher than that of H[2]O. This excess enthalpy of O[2] is the main reason for consistently negative heats of combustion and their large magnitudes. Electronegativities and Exothermicity of Combustion? The bond-enthalpy diagram in Figure 1, panel b reveals that an explanation of combustion exothermicity in terms of Pauling electronegativities(3) is not convincing. According to this theory, the reactant molecules with atoms of similar electronegativities and therefore weak bonds are converted into compounds (CO[2], H[2]O) that have strong bonds between atoms of very different electronegativities, and the energy difference is released as heat. (3) In reality, however, C-C and C-O bonds have similar strengths, see Figure 1, panel b, as do the bonds in CH[4] and CO[2], see Figure 1, panel a, in spite of the different electronegativies of C, H, and O. In addition, given that the electronegativity of N is also fairly different from those of C and H,(3) this theory would also predict reactions of the type 6 CH[4] + 7 N[2] - 8 NH[3] + 2 C[3]N[3] to be exothermic, while in reality they are endothermic (D[r]H^o = +426 kJ/ mol for the given reaction: natural gas does not react with the nitrogen in air; also see Figure SI2 for relevant bond enthalpies). General Heat of Combustion Analysis By applying our bond-enthalpy analysis to the combustion of a general organic compound containing C, H, and O,[ed-2015-00](4)we can derive a simple relation between D[c]H^o and the stoichiometric coefficient n[O[2]], as shown in eqs S1-S10 in the Supporting Information. The gist of the calculation can be understood based on Figure 1, panel b, which shows bond-formation enthalpies of double bonds in O[2] and C-O of CO[2] as well as of two single bonds in H[2]O and in organic fuels. First, we note that for every two C-H bonds, one molecule of H[2]O (with two O-H bonds) is formed, with DH^o of about -107 kJ/mol, see Figure 1, panel b. Thus, we can account for the number of bonds in H [2]O without involving bonds in O[2]. As a result, each bond in O[2] can be matched by a bond in CO[2] (see eq S4 in the Supporting Information); the conversion of O-O to a C-O bond in CO[2] is accompanied by an enthalpy change of -306 kJ/mol, which is the dominant contribution to the heat of combustion. In addition, one C-C, two C-C, or two C-O bonds of the fuel are also converted to a double bond in CO[2], with DH^o of about -115 kJ/mol. Next, we exploit that the number of all bonds in a hydrocarbon fuel equals the number of O[2] molecules (eq S9). In the products, every bond of O is half shared with C (in CO[2]) or H (in H[2]O). Thus, the reductions in enthalpy from two C-H bonds to H[2]O (-107 kJ/mol) and from two bonds not involving H to C-O in CO[2] (-115 kJ/mol), see Figure 1, panel b, average to about -111 kJ/mol for each mole of O [2], which adds to the -306 kJ/mol for each mole of O[2] resulting from the conversion to CO[2]. Together, this gives -417 kJ/mol for each mole of O[2], that is,[ed-2015-00](5) This is derived more rigorously in the Supporting Information. The analysis indicates that of the numerical factor in eq 5, one can attribute -306 kJ/mol, that is, about ^3/[4] of the heat of combustion, to the unusually high bond-formation enthalpy (i.e., weak bonds) of O[2], see Figure 1, panel b, while about -111 kJ/mol is due to the lower bond-formation enthalpies of H[2]O and CO[2] relative to H- and C-containing reactants, respectively. Eq 5 implies that about 417 kJ of heat is released per mole of O[2] consumed in a combustion reaction, as indicated in the title of the paper. Heat of Condensation of H[2]O In physical chemistry, the heat of combustion value is usually based on reaction to H[2]O(l), the state of H[2]O at standard conditions (298 K and 1 bar).(1-5) The conversion from H[2]O(g) to H[2]O(l) results in an enthalpy change of -44 kJ/mol, the heat of condensation, due to H-bond formation between H[2]O molecules. Thus, the prediction of the heat of combustion should include a simple second term from H[2]O condensation:[ed-2015-00](6)This corresponds to the "higher heating value" of the fuel, while eq 5 gives the "lower heating value".(7) Heat of Combustion from Elemental Composition The stoichiometric coefficients in the combustion reaction 4 are related to the elemental composition numbers c, h, o, and n of the fuel, C[c]H[h]O[o]N[n], according to(10)[ed-2015-00](7)[ed-2015-00] (8)Thus, we can rewrite eq 6 purely in terms of fuel composition as [ed-2015-00](9) The corresponding lower heating value, eq 5, is -417 kJ/mol (c + h/4 - o/2). In the following, we will show that eq 9 predicts most heats of combustion with an error of only a few percent. Note that eq 9 enables the prediction of the heat of combustion of complex fuel mixtures, such as gasoline, C[8]H[15], simply from their elemental composition, while previous approaches for calculating heats of combustion require knowledge of the molecular structures.(6-9) Comparison with Experimental Data Figure 2, panel a compares our simple predictions of D[c]H^o according to eq 9 (dashed line) with experimental heats of combustion compiled by Domalski,(10) plotted as a function of (n[O[2]] + 0.106 n [H[2]O(l)]), for over 500 compounds whose heteroatoms do not exceed the carbon atoms in number (i.e., c >= n + o). The data(10) include linear and cyclic aliphatic hydrocarbons, aromatics, alcohols, carbohydrates, linear and cyclic ethers, aldehydes, ketones, aliphatic, unsaturated, and aromatic acids, esters, steroids, lactones, amines, amides, amino acids, N-containing heterocycles, and porphyrines. The plot shows the predicted linear relation between D [c]H^o and (n[O[2]] + 0.106 n[H[2]O(l)]) with a slope of -418 kJ/mol (solid line), that is,[ed-2015-00](10)which agrees within 0.3% with the predicted -417 kJ/mol (dashed line) of eq 9. Figure 2 [ed-2015-00] Figure 2. (a) Heats of combustion plotted versus (n[O[2]] + 0.106 n[H [2]O(l)]) for 529 molecules(10) not dominated by heteroatoms (c >= o + n). Dashed line, theoretical prediction; solid line, best linear fit (see text). Five data points with larger heats of combustion are not shown but are also close to the theoretical prediction. The inset on the right shows data for smaller molecules with higher resolution. (b) Distribution of the ratio of measured and predicted heats of combustion. Open bars, all uncharged molecules in ref 10; filled bars, molecules not dominated by heteroatoms. A corresponding analysis only in terms of the number of carbon atoms in the fuel, shown in Figure SI3, gives less good agreement with the experimental values. High Resolution Image Download MS PowerPoint Slide The quality of the predictions can be further quantified in terms of the ratios of the measured and predicted (from eq 9) heats of combustion, (D[c]H^o)/(D[c]H^o)[pred]. Figure 2, panel b displays the histogram of the distribution of that ratio for all 663 molecules(10) (except those containing nitrates), shown as open bars, and for 529 molecules not dominated by heteroatoms, that is, with c >= n + o, plotted as filled bars. The ratios for the latter in particular are narrowly clustered, with an average at around 1.002, corresponding to the prefactor of -418 kJ/mol in eq 10, and a standard deviation from the mean of 3.1%. For larger molecules, the uncertainty is even smaller, for example, 2.1% for molecules with eight or more carbon atoms, based on 268 entries in Domalski's database,(10) with an average prefactor of -416 kJ/mol, again close to the predicted -417 kJ/mol of eq 9. This validates our analysis and makes it attractive for practical applications to complex molecules where experimental data may not be available or to fuels where only the elemental composition is known. Most of the outliers with >10% deviation in Figure 2, panel b are low-molar-mass compounds with small heats of combustion affected by special features such a triple bonds or ionic interactions. These are discussed in the Supporting Information together with the effects of nitrogen and sulfur. For the combustion of ammonia, the prediction by eq 10 is accurate within 1%. Aromatic stabilization actually improves the agreement with our prediction since it moves C-C bonds to lower enthalpy, closer to pairs of C-C bonds (see Figure 1b); for benzene, the prediction by eq 10 is accurate to within 0.2% (-3273 vs -3268 kJ /mol). Removal of Oxygen Atoms in Biofuel Production Oxygen or nitrogen atoms in a fuel reduce the energy density of the fuel since unlike C or H, they do not react with O[2] and thus do not increase the number of O[2] molecules in the combustion reaction. While N is only "dead weight" since the coefficient n of nitrogen does not show up in our eq 10, the presence of oxygen in the fuel actually reduces the magnitude of the heat of combustion by (418 kJ/ mol) o/2 in eq 10. For instance, glucose, C[6]H[12]O[6], has only 72% of the molar heat of combustion of cyclohexane, C[6]H[12].(10) Since glucose has a 2.14-times larger molar mass than cyclohexane, the heat of combustion per mass of glucose is only ^1/[3] of that of cyclohexane. This doubly undesirable effect of oxygen in the fuel on the combustion energy density is an important impetus for the removal of oxygen atoms in the production of biofuels such as ethanol or butanol from sugars such as glucose. Because of its oxygen atom, even ethanol still has a 15% smaller heat of combustion than ethane (-1366.7 vs -1558.3 kJ/mol,(10) respectively); per mass, its heat of combustion is only 62% of that of octane/gasoline (-29.7 vs -48 MJ/ kg, respectively). Further, our analysis reveals why oxygen atoms cannot be removed from sugars as O[2]: the high enthalpy of O[2], see Figure 1, would require an excessive energy input. Instead, in anaerobic fermentation or pyrolysis processes, some feedstock carbon or hydrogen is sacrificed as CO[2] or H[2]O,(20) which is energetically favorable according to Figure 1, panel b. "Energy-Rich" Molecules Combustion fuels such as octane, ethanol, or hydrogen are commonly regarded as molecules of high energy, which is sometimes summarized as the concept that a more reduced molecule or carbon atom has a higher energy.(21) However, this is misleading since the total bond enthalpy of CH[4] is actually slightly lower than that of CO[2], see Figure 1, panel a, and the listed fuels cannot give off significant energy in the absence of O[2] or F[2]. Therefore, instead of referring to the "energy density" of such fuels, one should use the term "combustion-energy density". Similarly, it is inconsistent for biochemistry textbooks to define the energy content of molecules in terms of bond energies and then refer to "energy-rich products such as starch and sucrose"(20) without mentioning the more energy-rich O [2] molecule. The analysis in Figure 1 clearly identifies O[2] as a particularly "energy-rich" molecule, crucial for making combustions strongly exothermic regardless of the composition of the organic fuel. Our treatment based on bond enthalpies provides simple, general explanations for various experimental observations. For instance, the diagram in Figure 1, panel b shows that molecules with C-C, H-H, and C-H bonds have rather similar enthalpies and thus readily explains why reactions between "fuels of high energy density" such as C and H [2] are in fact not strongly exothermic without O[2]. It also demonstrates that anaerobic fermentation of glucose to CO[2] and lactic acid or ethanol is only moderately exothermic because the enthalpy of a C-O double bond of CO[2] is only about -104 kJ/mol lower than that of two C-O or C-C bonds in glucose. O[2] in the Atmosphere Why is O[2] abundant in air despite its high enthalpy? Our analysis has shown that O[2] is unusually energy-rich, so the free energy of the atmosphere would be reduced if O[2] reacted away. Indeed, for the first 2 billion years of the earth's history, atmospheric levels of O [2] were low, less than 10% of today's value.(22) All the O[2] in the earth's atmosphere has been produced by photosynthesis in cyanobacteria, algae, and higher plants. It is interesting to note that O[2] is a by- or waste-product of photosynthetic H^+- and e^ --production from H[2]O.(22) The disadvantage of the production of O [2], which is energetically so unfavorable, is overcompensated by the ubiquitous availability of H[2]O as a proton and electron source for photosynthesizing organisms. It is the price that photosynthetic organisms have to pay (with "cheap" energy from the sun) to be able to live wherever H[2]O is present. In addition, they can later recover the energy of O[2] by cellular respiration.(22) These considerations show that atmospheric O[2] stores energy originating from the sun, and that the heat of combustion in air can be regarded as fossil solar energy, even when abiotically generated methane is involved. Finally, given the high bond enthalpy of O[2], one may wonder why N[2] in the atmosphere does not combust exothermically. An explanation mostly in terms of the high enthalpies of nitrogen-oxygen bonds is given in the Supporting Information. Teaching "What Makes Fire Hot" The insights and results presented here can be easily incorporated into chemistry courses at different levels. In a survey course, the questions "Why is fire hot?" or "What makes fire hot?" can now be answered by simply stating that the double bond in O[2] is unusually weak, compared to other double bonds or pairs of bonds, and that formation of the stronger bonds in H[2]O and CO[2] reduces the potential energy of the molecules, which results in the release of heat or an increase in the thermal motion of the gas molecules; this results in flame propagation under suitable heat- and mass-transfer conditions.(6) In a general chemistry course for chemistry majors, a more quantitative analysis in terms of bond energies or enthalpies can be included along the lines of Figure 1. In other words, here an additional question, "How much heat can be produced from combustion of a certain fuel?" can be answered. The heat of combustion per mole of O[2] used in the analysis can be rounded to -400 kJ/mol to keep the number simple, or it can be increased to -430 kJ/mol to get fairly good agreement with experimental data even without mentioning the effect of H[2]O condensation. The topic is attractive because it connects the areas of bond energies and thermochemistry in a context that students can relate to such as the combustion of gasoline or ethanol. In a thermodynamics course, one can quickly justify the formula for the heat of combustion, eq 6, based on the enthalpy differences between reactants and products as highlighted in Figure 1, panel b, plus the heat of condensation of H[2]O. In this fashion, I have successfully included the topic in my junior-level thermodynamics course. The excellent agreement with the large set of experimental data in Figure 2, which validates the simple formula, could be shared with physical chemistry students. In homework problems, one can ask students to quickly predict heats of combustion even of complex mixed fuels such as gasoline, C[8]H[15], simply from the elemental composition, or to explain why ethanol produces less combustion heat than the corresponding volume of gasoline (-23.2 MJ/L and ca. -33 MJ/ L, respectively). Conclusions ARTICLE SECTIONS Jump To --------------------------------------------------------------------- Our analysis provides simple answers to two related, important questions: "What makes fire hot?" and "How much heat is produced?" in the combustion of a certain fuel. One can now explain that the double bond in O[2] is unusually weak, and therefore the formation of the stronger bonds in CO[2] and H[2]O results in the release of heat or an increase in thermal motion. We have pointed out that in a general analysis of bond enthalpies, it is crucial to count electron-pair bonds so that the total number of bonds remains unchanged. This enables a general analysis of the enthalpy in the reactants and products per bond (or more conveniently per two bonds so that O[2] and H[2]O can be treated per molecule). We have confirmed by rigorous calculation and by analysis of an extensive database that the heat of combustion is close to -418 kJ/mol for each mole of O[2], of which -306 kJ/mol can be attributed to the weak double bond (less negative bond-formation enthalpy) of O[2] and the rest to the stronger bonds in H[2]O compared to two C-H bonds, and in CO[2] compared to two C-C or C-O bonds in the reactants. By taking into account the heat of condensation of H[2]O, -44 kJ/mol, our simple equation predicts heats of combustion with good precision, for example, +- 2.1% for molecules with >= 8 carbons. It can even be applied to complex mixed fuels for which only the elemental composition is known. The analysis reveals a doubly undesirable effect of oxygen atoms in a fuel and the prohibitive energetic cost of removing them as O[2], which is relevant in the context of biofuels. Generally, our analysis indicates that it is not the organic fuel but rather O[2] that is "energy-rich". The presence of large quantities of O[2] in the earth's atmosphere in spite of its high enthalpy is explained by photosynthesis from H[2]O, a ubiquitous proton and electron source for plants and algae. Supporting Information ARTICLE SECTIONS Jump To --------------------------------------------------------------------- The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.5b00333. * Derivation of eq 5; discussions of terminology and units for D[c] H^o, limited importance of CO[2] in making combustions exothermic, bond energies and bond-formation enthalpies, outliers and deviations from predicted behavior due to unusual structural features, analysis for nitrogen- and sulfur-containing compounds, and why the atmosphere does not combust spontaneously (PDF) * ed5b00333_si_001.pdf (814.4 kb) Terms & Conditions Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/ permissions.html. Author Information ARTICLE SECTIONS Jump To --------------------------------------------------------------------- * Corresponding Author + Klaus Schmidt-Rohr - Department of Chemistry, Brandeis University, Waltham, Massachusetts 02453, United States; Email: [email protected] * * * Notes The author declares no competing financial interest. References ARTICLE SECTIONS Jump To --------------------------------------------------------------------- This article references 22 other publications. 1. 1 Atkins, P.; de Paula, J. Physical Chemistry; 8th ed.; Freeman: New York, 2006. Google Scholar There is no corresponding record for this reference. 2. 2 Engel, T.; Reid, P. Physical Chemistry; 2nd ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2010. Google Scholar There is no corresponding record for this reference. 3. 3 Levine, I. N. Physical Chemistry; 5th ed.; McGraw-Hill: London, 2002. Google Scholar There is no corresponding record for this reference. 4. 4 McQuarrie, D. A.; Simon, J. D. Molecular Thermodynamics; University Science Books: Sausalito, CA, 1999. Google Scholar There is no corresponding record for this reference. 5. 5 Mortimer, R. G. Physical Chemistry; 3rd ed.; Elsevier: San Diego, 2008. Google Scholar There is no corresponding record for this reference. 6. 6 Glassman, I.; Yetter, R. A. Combustion; 4th ed.; Academic Press: Burlington, MA, 2007. Google Scholar There is no corresponding record for this reference. 7. 7 Kuo, K. K. Principles of Combustion; Wiley: New York, 1986. Google Scholar There is no corresponding record for this reference. 8. 8 Bartok, W.; Sarofim, A. F. Fossil Fuel Combustion-A Source Book; Wiley: New York, 1991. Google Scholar There is no corresponding record for this reference. 9. 9 Come, G.-M. Gas-Phase Thermal Reactions; Kluwer: Boston, 2001. [Crossref], Google Scholar There is no corresponding record for this reference. 10. 10 Domalski, E. S. Selected Values of Heats of Combustion and Heats of Formation of Organic Compounds Containing the Elements C, H, N, O, and P J. Phys. Chem. Ref. Data 1972, 1, 221- 277 DOI: 10.1063/1.3253099 [Crossref], [CAS], Google Scholar 10 Selected values of heats of combustion and heats of formation of organic compounds containing the elements carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur Domalski, Eugene S. Journal of Physical and Chemical Reference Data (1972), 1 (2), 221-77CODEN: JPCRBU; ISSN:0047-2689. A review with 596 refs. and values of the heats of combustion and heats of formation for 719 org. compds. including: aliphatic, alicyclic, aromatic, heterocyclic, organosulfur, and organophosphorus compds., steroids, alkaloids, porphyrins, peptides, and amino acids. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS&resolution= options&coi=1%3ACAS%3A528%3ADyaE38XlsVCmtL0%253D&md5= 1f8309e3e412833f9f8605d0d99e052d 11. 11 Lloyd, W. G.; Davenport, D. A. Applying Thermodynamics to Fossil Fuels J. Chem. Educ. 1980, 57, 56- 60 DOI: 10.1021/ed057p56 [ACS Full Text ACS Full Text], [CAS], Google Scholar 11 Applying thermodynamics to fossil fuels. Heats of combustion from elemental compositions Lloyd, William G.; Davenport, Derek A. Journal of Chemical Education (1980), 57 (1), 56-60CODEN: JCEDA8; ISSN:0021-9584. Application of thermodn. to the estn. of heats of formation and heats of combustion of the elemental compns. encountered in fossil fuels is discussed. The use of elemental compn. to predict heating values of fossil fuels is suggested. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS&resolution= options&coi=1%3ACAS%3A528%3ADyaL3cXht1Ort7g%253D&md5= 69ab263be2b2a221ea14a44bdbf552f4 12. 12 Friedl, A.; Padouvas, E.; Rotter, H.; Varmuza, K. Predicting of heating values of biomass fuel from elemental composition Anal. Chim. Acta 2005, 544, 191- 198 DOI: 10.1016/j.aca.2005.01.041 [Crossref], [CAS], Google Scholar 12 Prediction of heating values of biomass fuel from elemental composition Friedl, A.; Padouvas, E.; Rotter, H.; Varmuza, K. Analytica Chimica Acta (2005), 544 (1-2), 191-198CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.) The heating value of biomass is an important parameter for the design and the control of power plants using this type of fuel. The so-called higher heating value, HHV, is the enthalpy of complete combustion of a fuel including the condensation enthalpy of formed water. Numerous empirical equations were published to relate the heating value to the elemental compn. of fuels other than biomass. Data of 154 biomass samples of different origin (for instance wood, grass, rye, rape, reed, brewery waste, and poultry litter) were selected from the database BIOBIB. Each sample was characterized by the contents (in% of dry material) of carbon, hydrogen, nitrogen, oxygen, sulfur, chlorine and ash. PCA of these data shows a clustering according to the origin of the samples. A subset of 122 samples, all consisting of plant materials, was used to develop regression models for a prediction of HHV from the elemental compn. Models with best predictive ability were obtained using the contents of carbon, C; hydrogen, H; and nitrogen, N, and applying the methods OLS and PLS with the variables C, C2, H, C x H and N. The std. errors of prediction of the best new models are considerably smaller than those obtained with models found in literature. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS&resolution= options&coi=1%3ACAS%3A528%3ADC%252BD2MXltlelu7k%253D&md5= ca28bca435dae289925956c302ba447e 13. 13 Darwent, B. D. Bond Dissociation Energies in Simple Molecules Nat. Stand. Ref. Data. Ser., Natl. Bur. Stand. (U. S.) 1970, 31, 1- 52 Google Scholar There is no corresponding record for this reference. 14. 14 McMillen, D. F.; Golden, D. M. Hydrocarbon Bond Dissociation Energies Annu. Rev. Phys. Chem. 1982, 33, 493- 532 DOI: 10.1146/ annurev.pc.33.100182.002425 [Crossref], [CAS], Google Scholar 14 Hydrocarbon bond dissociation energies McMillen, Donald F.; Golden, David M. Annual Review of Physical Chemistry (1982), 33 (), 493-532CODEN: ARPLAP; ISSN:0066-426X. A review with 246 refs. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS&resolution= options&coi=1%3ACAS%3A528%3ADyaL3sXjtl2isA%253D%253D&md5= 35e1ddff0f54c268e50fe9f3dca68b40 15. 15 Blanksby, S. J.; Ellison, G. B. Bond Dissociation Energies of Organic Molecules Acc. Chem. Res. 2003, 36, 255- 263 DOI: 10.1021 /ar020230d [ACS Full Text ACS Full Text], [CAS], Google Scholar 15 Bond Dissociation Energies of Organic Molecules Blanksby, Stephen J.; Ellison, G. Barney Accounts of Chemical Research (2003), 36 (4), 255-263CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society) A review. In this Account the authors have compiled a list of reliable bond energies that are based on a set of critically evaluated expts. A brief description of the three most important exptl. techniques for measuring bond energies is provided. The authors demonstrate how these exptl. data can be applied to yield the heats of formation of org. radicals and the bond enthalpies of more than 100 representative org. mols. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS&resolution= options&coi=1%3ACAS%3A528%3ADC%252BD3sXmt1OqsA%253D%253D&md5= e313bd3c3a7809b70baa32c83e70d135 16. 16 McMurry, J.; Fay, R. C. Chemistry; 4th ed.; Pearson Prentice Hall : Upper Saddle River, NJ, 2004. Google Scholar There is no corresponding record for this reference. 17. 17 Benson, S. W. Bond Energies J. Chem. Educ. 1965, 42, 502- 518 DOI: 10.1021/ed042p502 [ACS Full Text ACS Full Text], [CAS], Google Scholar 17 Bond energies Benson, Sidney W. Journal of Chemical Education (1965), 42 (9), 502-18CODEN: JCEDA8 ; ISSN:0021-9584. A "resource paper" with an appreciation of the subject and an extensive bibliography. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS&resolution= options&coi=1%3ACAS%3A528%3ADyaF2MXkvVCjs78%253D&md5= 614f485efd4ff2e54ac0e49f5d0c81a2 18. 18 Moore, J. W.; Staniski, C. L.; Jurs, P. C. Chemistry-The Molecular Science; Brooks Cole: Belmont, CA, 2010. Google Scholar There is no corresponding record for this reference. 19. 19 Hill, J. W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry; 4th ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2005. Google Scholar There is no corresponding record for this reference. 20. 20 Lehninger, A. L.; Nelson, D. L.; Cox, M. M. Principles of Biochemistry; 2nd ed.; Worth Publishers: New York, 1993. Google Scholar There is no corresponding record for this reference. 21. 21 Karp, G. Cell and Molecular Biology: Concepts and Experiments; 6 th ed.; Wiley: Hoboken, NJ, 2009. Google Scholar There is no corresponding record for this reference. 22. 22 Lane, N. First breath: Earth's billion-year struggle for oxygen New Scientist 2010, 2746, 1- 6 Google Scholar There is no corresponding record for this reference. Cited By --------------------------------------------------------------------- This article is cited by 28 publications. 1. Thomas A. Corry, Patrick J. O'Malley. Localized Bond Orbital Analysis of the Bonds of O2. The Journal of Physical Chemistry A 2020, 124 (47) , 9771-9776. https://doi.org/10.1021/ acs.jpca.0c07836 2. Violeta A. Martinez, Jorge G. Ibanez. All Roads Lead to Rome: Triple Stoichiometry with a Lithium Battery. Journal of Chemical Education 2020, 97 (11) , 4103-4107. https://doi.org/10.1021/ acs.jchemed.0c00876 3. Klaus Schmidt-Rohr. Oxygen Is the High-Energy Molecule Powering Complex Multicellular Life: Fundamental Corrections to Traditional Bioenergetics. ACS Omega 2020, 5 (5) , 2221-2233. https://doi.org/10.1021/acsomega.9b03352 4. Orion Staples, Juan H. Leal, Patrick A. Cherry, Charles S. McEnally, Lisa D. Pfefferle, Troy A. Semelsberger, Andrew D. Sutton, Cameron M. Moore. Camphorane as a Renewable Diesel Blendstock Produced by Cyclodimerization of Myrcene. Energy & Fuels 2019, 33 (10) , 9949-9955. https://doi.org/10.1021/ acs.energyfuels.9b02557 5. Klaus Schmidt-Rohr. How Batteries Store and Release Energy: Explaining Basic Electrochemistry. Journal of Chemical Education 2018, 95 (10) , 1801-1810. https://doi.org/10.1021/ acs.jchemed.8b00479 6. Weston Thatcher Borden, Roald Hoffmann, Thijs Stuyver, and Bo Chen . Dioxygen: What Makes This Triplet Diradical Kinetically Persistent?. Journal of the American Chemical Society 2017, 139 (26) , 9010-9018. https://doi.org/10.1021/jacs.7b04232 7. Mingjian Wen, Samuel M. Blau, Evan Walter Clark Spotte-Smith, Shyam Dwaraknath, Kristin A. Persson. BonDNet: a graph neural network for the prediction of bond dissociation energies for charged molecules. 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Rashi Koul, Naveen Kumar, R.C Singh. A review on the production and physicochemical properties of renewable diesel and its comparison with biodiesel. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects 2019, 1 , 1-21. https:// doi.org/10.1080/15567036.2019.1646355 18. R.D. Merckel, F.J.W.J. Labuschagne, M.D. Heydenrych. Oxygen consumption as the definitive factor in predicting heat of combustion. Applied Energy 2019, 235 , 1041-1047. https://doi.org /10.1016/j.apenergy.2018.10.111 19. Husnugul Yilmaz Atay. Halogen-Free Flame Retardant Plastics. 2019 ,,, 3057-3079. https://doi.org/10.1007/978-3-319-68255-6_156 20. Paul R. Gregory, Andrew Martin, Boyce S. Chang, Stephanie Oyola-Reynoso, Jean-Francis Bloch, Martin M. Thuo. Inverting Thermal Degradation (iTD) of Paper Using Chemi- and Physi-Sorbed Modifiers for Templated Material Synthesis. Frontiers in Chemistry 2018, 6 https://doi.org/10.3389/fchem.2018.00338 21. Olivia Basu, Subhabrata Mukhopadhyay, Samar K Das. Cobalt based functional inorganic materials: Electrocatalytic water oxidation. Journal of Chemical Sciences 2018, 130 (7) https://doi.org/ 10.1007/s12039-018-1494-4 22. J. Galindo-de-la-Rosa, R. Balam-Vera, A. Alvarez, E. Ortiz-Ortega, N. Arjona, L.G. Arriaga, J. Ledesma-Garcia. Urease enzyme as anodic catalyst in a microfluidic fuel cell. Journal of Physics: Conference Series 2018, 1052 , 012057. https://doi.org/ 10.1088/1742-6596/1052/1/012057 23. Sean C. Rismiller, Melinda M. Groves, Min Meng, Yuan Dong, Jian Lin. Water assisted liquefaction of lignocellulose biomass by ReaxFF based molecular dynamic simulations. Fuel 2018, 215 , 835-843. https://doi.org/10.1016/j.fuel.2017.11.108 24. Xiaoyan Cao, George R. Aiken, Kenna D. Butler, Thomas G. Huntington, William M. Balch, Jingdong Mao, Klaus Schmidt-Rohr. Evidence for major input of riverine organic matter into the ocean. Organic Geochemistry 2018, 116 , 62-76. https://doi.org/ 10.1016/j.orggeochem.2017.11.001 25. 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RSC Advances 2016, 6 (106) , 103888-103894. https://doi.org/10.1039/C6RA22104A * Figures * References * Support Info * Abstract [ed-2015-00] High Resolution Image Download MS PowerPoint Slide Figure 1 [ed-2015-00] Figure 1. Bond-formation enthalpies of (a) four and (b) two moles of electron-pair bonds in reactants (left) and products (right) relevant for (a) combustion of hydrogen and of methane; (b) combustion of a general C-, H-, and O-containing organic fuel. Note that the bond-formation enthalpy of the double bond in O[2] is distinctly higher (less negative) than that of other pairs of bonds. High Resolution Image Download MS PowerPoint Slide Figure 2 [ed-2015-00] Figure 2. (a) Heats of combustion plotted versus (n[O[2]] + 0.106 n[H[2]O(l)]) for 529 molecules(10) not dominated by heteroatoms ( c >= o + n). Dashed line, theoretical prediction; solid line, best linear fit (see text). Five data points with larger heats of combustion are not shown but are also close to the theoretical prediction. The inset on the right shows data for smaller molecules with higher resolution. (b) Distribution of the ratio of measured and predicted heats of combustion. Open bars, all uncharged molecules in ref 10; filled bars, molecules not dominated by heteroatoms. A corresponding analysis only in terms of the number of carbon atoms in the fuel, shown in Figure SI3, gives less good agreement with the experimental values. High Resolution Image Download MS PowerPoint Slide * References ARTICLE SECTIONS Jump To ----------------------------------------------------------------- This article references 22 other publications. 1. 1 Atkins, P.; de Paula, J. Physical Chemistry; 8th ed.; Freeman : New York, 2006. Google Scholar There is no corresponding record for this reference. 2. 2 Engel, T.; Reid, P. Physical Chemistry; 2nd ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2010. Google Scholar There is no corresponding record for this reference. 3. 3 Levine, I. N. Physical Chemistry; 5th ed.; McGraw-Hill: London, 2002. Google Scholar There is no corresponding record for this reference. 4. 4 McQuarrie, D. A.; Simon, J. D. Molecular Thermodynamics; University Science Books: Sausalito, CA, 1999. Google Scholar There is no corresponding record for this reference. 5. 5 Mortimer, R. G. Physical Chemistry; 3rd ed.; Elsevier: San Diego, 2008. Google Scholar There is no corresponding record for this reference. 6. 6 Glassman, I.; Yetter, R. A. Combustion; 4th ed.; Academic Press: Burlington, MA, 2007. Google Scholar There is no corresponding record for this reference. 7. 7 Kuo, K. K. Principles of Combustion; Wiley: New York, 1986. Google Scholar There is no corresponding record for this reference. 8. 8 Bartok, W.; Sarofim, A. F. Fossil Fuel Combustion-A Source Book; Wiley: New York, 1991. Google Scholar There is no corresponding record for this reference. 9. 9 Come, G.-M. Gas-Phase Thermal Reactions; Kluwer: Boston, 2001 . [Crossref], Google Scholar There is no corresponding record for this reference. 10. 10 Domalski, E. S. Selected Values of Heats of Combustion and Heats of Formation of Organic Compounds Containing the Elements C, H, N, O, and P J. Phys. Chem. Ref. Data 1972, 1, 221- 277 DOI: 10.1063/1.3253099 [Crossref], [CAS], Google Scholar 10 Selected values of heats of combustion and heats of formation of organic compounds containing the elements carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur Domalski, Eugene S. Journal of Physical and Chemical Reference Data (1972), 1 (2 ), 221-77CODEN: JPCRBU; ISSN:0047-2689. A review with 596 refs. and values of the heats of combustion and heats of formation for 719 org. compds. including: aliphatic, alicyclic, aromatic, heterocyclic, organosulfur, and organophosphorus compds., steroids, alkaloids, porphyrins, peptides, and amino acids. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS& resolution=options&coi=1%3ACAS%3A528%3ADyaE38XlsVCmtL0%253D& md5=1f8309e3e412833f9f8605d0d99e052d 11. 11 Lloyd, W. G.; Davenport, D. A. Applying Thermodynamics to Fossil Fuels J. Chem. Educ. 1980, 57, 56- 60 DOI: 10.1021/ ed057p56 [ACS Full Text ACS Full Text], [CAS], Google Scholar 11 Applying thermodynamics to fossil fuels. Heats of combustion from elemental compositions Lloyd, William G.; Davenport, Derek A. Journal of Chemical Education (1980), 57 (1), 56-60CODEN: JCEDA8; ISSN:0021-9584. Application of thermodn. to the estn. of heats of formation and heats of combustion of the elemental compns. encountered in fossil fuels is discussed. The use of elemental compn. to predict heating values of fossil fuels is suggested. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS& resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXht1Ort7g%253D& md5=69ab263be2b2a221ea14a44bdbf552f4 12. 12 Friedl, A.; Padouvas, E.; Rotter, H.; Varmuza, K. Predicting of heating values of biomass fuel from elemental composition Anal. Chim. Acta 2005, 544, 191- 198 DOI: 10.1016/ j.aca.2005.01.041 [Crossref], [CAS], Google Scholar 12 Prediction of heating values of biomass fuel from elemental composition Friedl, A.; Padouvas, E.; Rotter, H.; Varmuza, K. Analytica Chimica Acta (2005), 544 (1-2), 191-198CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.) The heating value of biomass is an important parameter for the design and the control of power plants using this type of fuel. The so-called higher heating value, HHV, is the enthalpy of complete combustion of a fuel including the condensation enthalpy of formed water. Numerous empirical equations were published to relate the heating value to the elemental compn. of fuels other than biomass. Data of 154 biomass samples of different origin (for instance wood, grass, rye, rape, reed, brewery waste, and poultry litter) were selected from the database BIOBIB. Each sample was characterized by the contents (in% of dry material) of carbon, hydrogen, nitrogen, oxygen, sulfur, chlorine and ash. PCA of these data shows a clustering according to the origin of the samples. A subset of 122 samples, all consisting of plant materials, was used to develop regression models for a prediction of HHV from the elemental compn. Models with best predictive ability were obtained using the contents of carbon, C; hydrogen, H; and nitrogen, N, and applying the methods OLS and PLS with the variables C, C2, H, C x H and N. The std. errors of prediction of the best new models are considerably smaller than those obtained with models found in literature. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS& resolution=options&coi= 1%3ACAS%3A528%3ADC%252BD2MXltlelu7k%253D&md5= ca28bca435dae289925956c302ba447e 13. 13 Darwent, B. D. Bond Dissociation Energies in Simple Molecules Nat. Stand. Ref. Data. Ser., Natl. Bur. Stand. (U. S.) 1970, 31, 1- 52 Google Scholar There is no corresponding record for this reference. 14. 14 McMillen, D. F.; Golden, D. M. Hydrocarbon Bond Dissociation Energies Annu. Rev. Phys. Chem. 1982, 33, 493- 532 DOI: 10.1146/annurev.pc.33.100182.002425 [Crossref], [CAS], Google Scholar 14 Hydrocarbon bond dissociation energies McMillen, Donald F.; Golden, David M. Annual Review of Physical Chemistry (1982), 33 (), 493-532 CODEN: ARPLAP; ISSN:0066-426X. A review with 246 refs. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS& resolution=options&coi= 1%3ACAS%3A528%3ADyaL3sXjtl2isA%253D%253D&md5= 35e1ddff0f54c268e50fe9f3dca68b40 15. 15 Blanksby, S. J.; Ellison, G. B. Bond Dissociation Energies of Organic Molecules Acc. Chem. Res. 2003, 36, 255- 263 DOI: 10.1021/ar020230d [ACS Full Text ACS Full Text], [CAS], Google Scholar 15 Bond Dissociation Energies of Organic Molecules Blanksby, Stephen J.; Ellison, G. Barney Accounts of Chemical Research (2003), 36 (4), 255-263CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society) A review. In this Account the authors have compiled a list of reliable bond energies that are based on a set of critically evaluated expts. A brief description of the three most important exptl. techniques for measuring bond energies is provided. The authors demonstrate how these exptl. data can be applied to yield the heats of formation of org. radicals and the bond enthalpies of more than 100 representative org. mols. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS& resolution=options&coi= 1%3ACAS%3A528%3ADC%252BD3sXmt1OqsA%253D%253D&md5= e313bd3c3a7809b70baa32c83e70d135 16. 16 McMurry, J.; Fay, R. C. Chemistry; 4th ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2004. Google Scholar There is no corresponding record for this reference. 17. 17 Benson, S. W. Bond Energies J. Chem. Educ. 1965, 42, 502- 518 DOI: 10.1021/ed042p502 [ACS Full Text ACS Full Text], [CAS], Google Scholar 17 Bond energies Benson, Sidney W. Journal of Chemical Education (1965), 42 (9), 502-18CODEN: JCEDA8; ISSN:0021-9584. A "resource paper" with an appreciation of the subject and an extensive bibliography. >> More from SciFinder ^(r) https://chemport.cas.org/services/resolver?origin=ACS& resolution=options&coi=1%3ACAS%3A528%3ADyaF2MXkvVCjs78%253D& md5=614f485efd4ff2e54ac0e49f5d0c81a2 18. 18 Moore, J. W.; Staniski, C. L.; Jurs, P. C. Chemistry-The Molecular Science; Brooks Cole: Belmont, CA, 2010. Google Scholar There is no corresponding record for this reference. 19. 19 Hill, J. W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry; 4th ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2005. Google Scholar There is no corresponding record for this reference. 20. 20 Lehninger, A. L.; Nelson, D. L.; Cox, M. M. Principles of Biochemistry; 2nd ed.; Worth Publishers: New York, 1993. Google Scholar There is no corresponding record for this reference. 21. 21 Karp, G. Cell and Molecular Biology: Concepts and Experiments ; 6th ed.; Wiley: Hoboken, NJ, 2009. Google Scholar There is no corresponding record for this reference. 22. 22 Lane, N. First breath: Earth's billion-year struggle for oxygen New Scientist 2010, 2746, 1- 6 Google Scholar There is no corresponding record for this reference. * Supporting Information Supporting Information ARTICLE SECTIONS Jump To ----------------------------------------------------------------- The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.5b00333. + Derivation of eq 5; discussions of terminology and units for D[c]H^o, limited importance of CO[2] in making combustions exothermic, bond energies and bond-formation enthalpies, outliers and deviations from predicted behavior due to unusual structural features, analysis for nitrogen- and sulfur-containing compounds, and why the atmosphere does not combust spontaneously (PDF) + ed5b00333_si_001.pdf (814.4 kb) Terms & Conditions Most electronic Supporting Information files are available without a subscription to ACS Web Editions. 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