Nitrogen bond enthalpy

Draw the Lewis structure for the hypothetical molecule N6, consisting of a six-membered ring of nitrogen atoms. Using bond enthalpies, calculate the enthalpy of reaction for the decomposition of N6 to N2(g). Do you expect N6 to be a stable molecule ... 

A The calculation of the bond enthalpy term for nitrogen-fluorine bonds in NF3 is ... 

The most stable state of nitrogen in acidic solution is the ammonium ion, NH4(aq), which is isoelectronic with CH4 and H30+. It is a tetrahedral ion with strong N-H bonds. The mean N-H bond enthalpy in NH4(aq) is 506 kJ mol 1 (that of the O-H bonds in H30 + is 539 kJ mol" ). The enthalpy of hydration of the ammonium ion is — 345 kJ mol V This value placed into the Born equation (3.32) gives an estimate of the radius of the ammonium ion of 135 pm, a value insignificantly different from its thermochemical radius of 136 pm. The value is comparable to that estimated for the smaller H30+ ion (99 pm) from its more negative enthalpy of hydration (— 420 kJ mol -see Section 2.6.1). The proton affinity of the ammonia molecule is of interest in a comparison of its properties with those of the water molecule. The proton affinity is defined as the standard enthalpy change for the reaction ... 

The enthalpies of formation of phenols with nitrogen-bonded substituents appear in Table 4. 

The bond dissociation enthalpies for the nitrogen-nitrogen bond in N2 and [N2] are 945 and 765kJmol respectively. Acconnt for this difference in terms of MO theory, and... 

Through these simulations, students appreciate the energetic and kinetic aspects of chemical reactions and why the composition of the atmosphere is critical to the outcome. For example, the class simulates the effect on the yield of amino acids if the atmospheric composition was CO2 instead of CH4 or the nitrogen source was N2 instead of NH3. The simulations also allow students to investigate the consequences if the pre-biotic atmosphere contained free 02. Through these simulations, basic chemical concepts are discussed including thermodynamics, thermochemistry and bond enthalpies, kinetics, and catalysis. 

The driving force for such reactions is the loss of multiple-bond enthalpy. Addition reactions of this type may be involved in the formation of sulfur-nitrogen oligomers. 

Tlie enthalpy change for the equation showing aiiuiionia dissociating into a nitrogen atom and tliree hydrogen atoms is equal to tlu ee times the average bond enthalpy of the N-H bond (Wliy three ). 

The N2 molecule is verj unreactive because of the strong triple bond between nitrogen atoms (the N=N bond enthalpy is 941 kj/mol, nearly twice that for the bond in O2 Table 8.4). When substances burn in air, they normally react with O2 but not with N2. When magnesium burns in air, however, it reacts with N2 to form magnesium nitride (Mg3N2) ... 

Electron configurations in molecules can also be related to bond distances and bond enthalpies, aao (Section 8.8) As bond order increases, bond distances decrease and bond enthalpies increase. N2, for example, whose bond order is 3, has a short bond distance and a large bond enthalpy. The N2 molecule does not react readily with other substances to form nitrogen compounds. The high bond order of the molecule helps explain its exceptional stability. We should also note, however, that molecules with the same bond orders do not have the same bond distances and bond enthalpies. Bond order is only one factor influencing these properties. Other factors include nuclear charge and extent of orbital overlap. 

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