O-H Bonding (and ion dissociation)

[pzona]

This is probably something I should know, but I don't want to wait and ask my professor. In the combustion of H2, assuming O2 is plentiful enough not to be a limiting reactant, H2O forms as a result of the O-H bond being more stable than the bonds between two H or two O. Is this due to the electronegativity difference?

On a related note, although the answer might be the same, in a hydroxide's dissociation in a solution (let's say the dissociation of NaOH into Na^{+} and OH^{-} in water), the OH^{-} ion remains held together because of this bond, which is due to the difference in electronegativities, correct (aside from the fact that there isn't enough energy to break it)? And if so, what equation would I use to calculate the temperature or kinetic energy of the water needed to dissociate it further into H^{+} and O^{2-}?

 

[chemisttree]

This is probably something I should know, but I don't want to wait and ask my professor. In the combustion of H2, assuming O2 is plentiful enough not to be a limiting reactant, H2O forms as a result of the O-H bond being more stable than the bonds between two H or two O. Is this due to the electronegativity difference?

The electronegativity difference will tell you which atom gives an electron and which accepts the electron and perhaps the polarity of the resulting bond but is doesn't say anything about stability per se. It has to do with the energy level of the molecular bond vs the energy level of the individual atomic orbitals.

On a related note, although the answer might be the same, in a hydroxide's dissociation in a solution (let's say the dissociation of NaOH into Na^{+} and OH^{-} in water), the OH^{-} ion remains held together because of this bond, which is due to the difference in electronegativities, correct (aside from the fact that there isn't enough energy to break it)?

Not really... that OH- group swaps out that hydrogen with the solvent. In this case, it can also swap out the oxygen!

for example:

OH- + HOH <------> HOH + OH-
or
OH- + HOH <--------> OH- + HOH

 

[pzona]

Okay that leads me to another question then. In another polar solvent, such as THF, does the NaOH dissociate in the same way? And if so why?

 

[PhaseShifter]

It still dissociates, although solvation is generally different for ionic compounds in protic vs. aprotic solvents since aprotic solvents don't have hydrogens that can participate in hydrogen bonding..

 

[chemisttree]

Okay that leads me to another question then. In another polar solvent, such as THF, does the NaOH dissociate in the same way? And if so why?

NaOH ionizes into Na+ and OH- but the hydrogen and the oxygen do not swap out with the oxygen and hydrogens of THF.