Bonding average bond energies

Bond Average bond energy/kj moT Bond Average bond energy/kJ moP ... 

B = Average bond energy of P-CI bond. From the cycle it follows that ... 

Born-Haber cycle A thermodynamic cycle derived by application of Hess s law. Commonly used to calculate lattice energies of ionic solids and average bond energies of covalent compounds. E.g. NaCl ... 

For many purposes, for example the estimation of approximate heats of formation (p. 63), it is sufficient to have an average value. This average of the bond dissociation energies is called the average thermochemical bond energy or (more commonly) simply the bond energy. ... 

Strictly, these values are bond enthalpies, but the term energies is commonly used. Other descriptions are average standard bond energies, mean bond energies . 

Bond In compound Average thermochemical bond energy (kJ mol" )... 

Figure 4 Time step dependence of the average total energy for two models of a partially hydrated dodecamer DNA duplex. Thinner traces show results for virtually harmonic conditions when temperature was lowered to 1 K. The DNA molecule has fixed bond lengths, rigid bases, and fixed valence angles except for the mtra- and extracyclic bond angles m sugars, (a) No modifications of inertia (b) inertia modified as explained m the text. (From Ref. 54.)...

The view has also existed in the past that the carbon-silicon bond should be similar in behaviour to the carbon-carbon bond and would have a similar average bond energy. There is some measure of truth in the assumption about average bond energy but because silicon is more electropositive than carbon the C—Si bond will be polar and its properties will be very dependent on the nature of groups attached to the carbon and silicon groups. For example, the CH3—Si group is particularly resistant to oxidation but H13—Si is not. 

Extensive reviews of the effects of fluonnation on stmeture and bonding are available [75, 76, 77], and only the charactenstic trends in bond strengths will be covered here. The bond energies cited are average values corrected for the revised heats of formation of alkyl radicals [78], but their precision is seldom better than 2 kcal/mol for the fluoro compounds. 

Tables 2.3 and 2.4 list a selection of typical dissociation energies. The values given in Table 2.4 are average dissociation energies for a number of different molecules. For instance, the strength quoted for a C—O single bond is the average strength of such bonds in a selection of organic molecules, such as methanol (CH3—OH), ethanol (CH,CH2—OH), and dimethyl ether (CH,—O—Cl l5). The values should therefore be regarded as typical rather than as accurate values for a particular molecule.

Neglecting the possibility that the bond energy in primary amines be slightly less than in secondary and tertiary amines, we take the average value 2.88 v. e. for C N. 

Tabie 6 gives average bond energies for a variety of chemical bonds. The table has the following features ... 

Now we apply Equation, using average bond energy values from Table 6-2 - reaction — / j -S - bondsbroken - bonds formed A table helps us... 

Based on average bond energies, what energy change accompanies the formation of one mole of vinyl chloride Does the synthesis require an input of energy ... 

C06-0060. Use average bond energies to estimate the energy change for the reaction of N2 and O2 to give... 

C06-0094. Use average bond energies (Table 6-2) to compare the stabilities of ethanol, C2 H5 OH, and dimethyl ether, (CH3)2 O, which have the same empirical formula, C2 Hg O (all the bonds are single bonds). 

C06-0095. Use average bond energies (Table 6-2) to compare the stabilities of allyl alcohol,... 

C06-0129. Use average bond energies (see Table 6-2) to estimate the net energy change per mole of silicon for the conversion of a silicon chain into an Si—O—Si chain. Repeat this calculation to estimate the net energy change per mole of carbon for the conversion of a carbon chain into a C—O—C chain. 

C06-0136. The heat required to sustain animais that hibernate comes from the biochemicai combustion of fatty acids, one of which is arachidonic acid. For this acid, (a) determine its structurai formuia (b) write its baianced combustion reaction (c) use average bond energies to estimate the energy released in the combustion reaction and (d) caicuiate the mass of arachidonic acid needed to warm a 500-kg bear from 5 to 25 °C. (Assume that the average heat capacity of bear flesh is 4.18 J/g K.)... 

Dispersion forces, dipole Interactions, and hydrogen bonds all are significantly weaker than covalent Intramolecular bonds. For example, the average C—C bond energy Is 345 kJ/mol, whereas dispersion forces are just 0.1 to 5 kJ/mol for small alkanes such as propane. Dipolar Interactions between polar molecules such as ace-tone range between 5 and 20 kJ/mol, and hydrogen bonds range between 5 and 50 kJ/mol. 

---