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The source for the N-N bond dissociation energy of 240 kJ/mol in the table
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Muhammed Irshad Shahul Hameed
The source for the N-N bond dissociation energy of 240 kJ/mol in the table
Your question about the source of Table 7.1 is correctly answered by the andselisk's comment. The value of $\pu{240 kJ\:mol-1}$ for $\ce{N-N}$ bond is probably initiated from Encyclopedia of Inorganic Chemistry, which has listed bond energies of wide variety of bonds and their respective bond lengths. It has given two values for $D_\circ$ of $\ce{N-N}$ bond: ~$\pu{167 kJ\:mol-1}$ for $\ce{N2H4}$ in general and $\pu{247\pm 13 kJ\:mol-1}$ for $\ce{H2N-NH2}$ in particular.
The reason is given in the very first paragraph of the article. In their words:
There are two different ways to define the bond energy even for the simplest diatomic molecule (see the diagram below). $\Delta D_{\circ'}$ is the dissociation energy measured from the very bottom of the potential energy well. However, the molecule possesses zero-point energy and thus, the experimentally measured dissociation energy $\Delta D_{\circ}$ is somewhat less:
In poly atomic compound there are other considerations. For example, the mean bond energy of $\ce{N-H}$ is the average of three bond energies associated with sequential fission of the three $\ce{N-H}$ bonds in ammonia ($\ce{NH3}$). These three values are different from each other and also different from their average, the mean bond energy of $\ce{N-H}$. Using this mean bond energy of $\ce{N-H}$ in $\ce{NH3}$ and the heat of atomization of $\ce{H2N-NH2}$, a value of $\pu{159 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. Then again, using the mean bond energy of $\ce{N-F}$ in $\ce{NF3}$ and the heat of atomization of $\ce{F2N-NF2}$, a value of $\pu{172 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. These two values are in somewhat good agreement. However, the dissociation of the two molecules are quite different:
Therefore, it is warned that care should be exercised in using any values of the bond energies.
Source:
R. Bruce King (Editor in chief), "Bond Energies," Encyclopedia of Inorganic Chemistry; 2nd Edition, John Wiley & Sons, Ltd.: New York, NY, 2005 (ISBN: 978-0-470-86078-6). Bond Energies is available online: https://doi.org/10.1002/0470862106.id098
Your question about the source of Table 7.1 is correctly answered by the andselisk's comment. The value of $\pu{240 kJ\:mol-1}$ for $\ce{N-N}$ bond is probably initiated from Encyclopedia of Inorganic Chemistry, which has listed bond energies of wide variety of bonds and their respective bond lengths. It has given two values for $D_\circ$ of $\ce{N-N}$ bond: ~$\pu{167 kJ\:mol-1}$ for $\ce{N2H4}$ in general and $\pu{247\pm 13 kJ\:mol-1}$ for $\ce{H2N-NH2}$ in particular.
The reason is given in the very first paragraph of the article. In their words:
There are two different ways to define the bond energy even for the simplest diatomic molecule (see the diagram below). $\Delta D_{\circ'}$ is the dissociation energy measured from the very bottom of the potential energy well. However, the molecule possesses zero-point energy and thus, the experimentally measured dissociation energy $\Delta D_{\circ}$ is somewhat less:
In poly atomic compound there are other considerations. For example, the mean bond energy of $\ce{N-H}$ is the average of three bond energies associated with sequential fission of the three $\ce{N-H}$ bonds in ammonia ($\ce{NH3}$). These three values are different from each other and also different from their average, the mean bond energy of $\ce{N-H}$. Using this mean bond energy of $\ce{N-H}$ in $\ce{NH3}$ and the heat of atomization of $\ce{H2N-NH2}$, a value of $\pu{159 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. Then again, using the mean bond energy of $\ce{N-F}$ in $\ce{NF3}$ and the heat of atomization of $\ce{F2N-NF2}$, a value of $\pu{172 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. These two values are in somewhat good agreement. However, the dissociation of the two molecules are quite different:
Therefore, it is warned that care should be exercised in using any values of the bond energies.
Source:
R. Bruce King (Editor in chief), "Bond Energies," Encyclopedia of Inorganic Chemistry; 2nd Edition, John Wiley & Sons, Ltd.: New York, NY, 2005 (ISBN: 978-0-470-86078-6). Bond Energies is available online: https://doi.org/10.1002/0470862106.id098
So once the N-N bond in hydrazine is broken, the N-H bonds are much weaker than they would be in ammonia? I like talking about bond dissociation energies in a General Chemistry setting, but always say it is a crude estimate. Even so, I think it is helpful in e.g. understanding how elemental oxygen is a reagent in many exothermic reactions while elemental nitrogen is not (at least not with the reaction partners that are sitting out on the shelf - I guess if they reacted with elemental nitrogen, they would not be sitting there anymore).More
Your question about the source of Table 7.1 is correctly answered by the andselisk's comment. The value of $\pu{240 kJ\:mol-1}$ for $\ce{N-N}$ bond is probably initiated from Encyclopedia of Inorganic Chemistry, which has listed bond energies of wide variety of bonds and their respective bond lengths. It has given two values for $D_\circ$ of $\ce{N-N}$ bond: ~$\pu{167 kJ\:mol-1}$ for $\ce{N2H4}$ in general and $\pu{247\pm 13 kJ\:mol-1}$ for $\ce{H2N-NH2}$ in particular.
The reason is given in the very first paragraph of the article. In their words:
In poly atomic compound there are other considerations. For example, the mean bond energy of $\ce{N-H}$ is the average of three bond energies associated with sequential fission of the three $\ce{N-H}$ bonds in ammonia ($\ce{NH3}$). These three values are different from each other and also different from their average, the mean bond energy of $\ce{N-H}$. Using this mean bond energy of $\ce{N-H}$ in $\ce{NH3}$ and the heat of atomization of $\ce{H2N-NH2}$, a value of $\pu{159 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. Then again, using the mean bond energy of $\ce{N-F}$ in $\ce{NF3}$ and the heat of atomization of $\ce{F2N-NF2}$, a value of $\pu{172 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. These two values are in somewhat good agreement. However, the dissociation of the two molecules are quite different:
$$\ce{H2N-NH2 -> 2 H2N^.} \qquad \pu{247 kJ\:mol-1}$$ $$\ce{F2N-NF2 -> 2 F2N^.} \qquad \pu{88 kJ\:mol-1}$$
Therefore, it is warned that care should be exercised in using any values of the bond energies.
Source:
R. Bruce King (Editor in chief), "Bond Energies," Encyclopedia of Inorganic Chemistry; 2nd Edition, John Wiley & Sons, Ltd.: New York, NY, 2005 (ISBN: 978-0-470-86078-6). Bond Energies is available online: https://doi.org/10.1002/0470862106.id098
Your question about the source of Table 7.1 is correctly answered by the andselisk's comment. The value of $\pu{240 kJ\:mol-1}$ for $\ce{N-N}$ bond is probably initiated from Encyclopedia of Inorganic Chemistry, which has listed bond energies of wide variety of bonds and their respective bond lengths. It has given two values for $D_\circ$ of $\ce{N-N}$ bond: ~$\pu{167 kJ\:mol-1}$ for $\ce{N2H4}$ in general and $\pu{247\pm 13 kJ\:mol-1}$ for $\ce{H2N-NH2}$ in particular.
The reason is given in the very first paragraph of the article. In their words:
In poly atomic compound there are other considerations. For example, the mean bond energy of $\ce{N-H}$ is the average of three bond energies associated with sequential fission of the three $\ce{N-H}$ bonds in ammonia ($\ce{NH3}$). These three values are different from each other and also different from their average, the mean bond energy of $\ce{N-H}$. Using this mean bond energy of $\ce{N-H}$ in $\ce{NH3}$ and the heat of atomization of $\ce{H2N-NH2}$, a value of $\pu{159 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. Then again, using the mean bond energy of $\ce{N-F}$ in $\ce{NF3}$ and the heat of atomization of $\ce{F2N-NF2}$, a value of $\pu{172 kJ\:mol-1}$ has been found for the $\ce{N-N}$ single bond energy. These two values are in somewhat good agreement. However, the dissociation of the two molecules are quite different:
$$\ce{H2N-NH2 -> 2 H2N^.} \qquad \pu{247 kJ\:mol-1}$$$$\ce{F2N-NF2 -> 2 F2N^.} \qquad \pu{88 kJ\:mol-1}$$
Therefore, it is warned that care should be exercised in using any values of the bond energies.
Source:
R. Bruce King (Editor in chief), "Bond Energies," Encyclopedia of Inorganic Chemistry; 2nd Edition, John Wiley & Sons, Ltd.: New York, NY, 2005 (ISBN: 978-0-470-86078-6). Bond Energies is available online: https://doi.org/10.1002/0470862106.id098
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