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Although the two bonds are the equivalent in the original symmetric molecule, the bond-dissociation energy of an oxygen–hydrogen bond varies slightly depending on whether or not there is another hydrogen atom bonded to the oxygen atom. Thus, the bond energy of a molecule of water is 461.5 kJ/mol (110.3 kcal/mol). [8]
Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes. [44] Hydrogen bonds between water molecules have an average lifetime of 10 −11 seconds, or 10 picoseconds. [45]
The thermodynamic basis of this low reactivity is the very strong H–H bond, with a bond dissociation energy of 435.7 kJ/mol. [83] It does form coordination complexes called dihydrogen complexes. These species provide insights into the early steps in the interactions of hydrogen with metal catalysts.
Liquid hydrogen also has a much higher specific energy than gasoline, natural gas, or diesel. [12] The density of liquid hydrogen is only 70.85 kg/m 3 (at 20 K), a relative density of just 0.07. Although the specific energy is more than twice that of other fuels, this gives it a remarkably low volumetric energy density, many fold lower.
The bond between the nitrogen and each oxygen is a double bond in one structure and a single bond in the other two, so that the average bond order for each N–O interaction is 2 + 1 + 1 / 3 = 4 / 3 . [8]
Such thermal energy manifests itself, however, in changes in the non-chemical state variables (such as temperature, pressure, volume) of the joint systems, as well as the changes in the mole numbers of the chemical constituents that describe the chemical reaction. [citation needed] Internal energy is defined with respect to some standard state.
The molecules of water are constantly moving concerning each other, and the hydrogen bonds are continually breaking and reforming at timescales faster than 200 femtoseconds (2 × 10 −13 seconds). [27] However, these bonds are strong enough to create many of the peculiar properties of water, some of which make it integral to life.
Bonding in + can be described as a covalent one-electron bond, which has a formal bond order of one half. [3] The ground state energy of the ion is -0.597 Hartree. [4] The bond length in the ground state is 2.00 Bohr radius.