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2 O reveals four different energy levels that correspond to the ionization energies of the two bonding and two nonbonding pairs of elections at 12.6eV, 14.7eV, 18.5eV, and 32.2eV. [1] This suggest that neither the two O-H bonds nor the two sp 3 lone pairs are degenerate in energy.
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]
The ab initio binding energy between the two water molecules is estimated to be 5-6 kcal/mol, although values between 3 and 8 have been obtained depending on the method. . The experimentally measured dissociation energy (including nuclear quantum effects) of (H 2 O) 2 and (D 2 O) 2 are 3.16 ± 0.03 kcal/mol (13.22 ± 0.12 kJ/mol) [5] and 3.56 ± 0.03 kcal/mol (14.88 ± 0.12 kJ/mol), [6] respectiv
The hydrogen bonds of water are around 23 kJ/mol (compared to a covalent O-H bond at 492 kJ/mol). Of this, it is estimated that 90% is attributable to electrostatics, while the remaining 10% is partially covalent. [95] These bonds are the cause of water's high surface tension [96] and capillary forces.
The standard Gibbs free energy of formation (G f °) of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 °C).
On the other hand, the molecules in liquid water are held together by relatively strong hydrogen bonds, and its enthalpy of vaporization, 40.65 kJ/mol, is more than five times the energy required to heat the same quantity of water from 0 °C to 100 °C (c p = 75.3 J/K·mol).
Bond strength: 492.215 kJ/mol O–H bond dissociation energy [3] Bond length: 95.87 pm ... Water/steam data table at triple point pressure ...
Owing to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to otherwise similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four. [41]