[Kdub]

We did any experiment where we wanted to find the heat of formation of water from the addition of phenol (weak acid) to a strong base (NaOH).

We have to explain why we get an overall endothermic reaction (heat of formation is a positive value).

what is said was:

As we can see, we end up with an endothermic absorption of energy when forming water. This is surely because there are hardly any hydrogen ions from phenol ionized and thus forcing it to bond with hydroxide requires energy instead of giving off energy.

Is that correct? do any of you have anything to add?
Thanks

[Jose M.]

Hi. Happy new year !

I understand that what you say is correct.

The weak acid, phenol, is an alcohol. Its a type of alcohol called an enol; an enol is an alcohol in which the OH is bonded to one of the sp2 hybridized carbons. Phenol is an aromatic (stable) alcohol. An aromatic compound is an organic (with carbon) compound that is cyclic and very stable because of its number of pi electrons (the other type are sigma electrons). Because it is stable, its little reactive. In chemistry, stable & reactive are opposites. Phenol is an even weaker acid, because its little reactive. Phenol doesnt react completely and its strengh is measured by Ka and also pKa (pKa is negative log of Ka). Phenol is aromatic, and an alcohol derived from benzene, the parent aromatic hydrocarbon. In organic chemistry, aromatic and aromaticity have nothing to do with odour; rather, it refers to stability of the cyclic compound.

In acid-base chemistry, pH is negative log of the concentration of H+. The neutral pH is 7. Below 7 is acid. Above 7 is alkaline (basic).

An endothermic reaction has a positive delta H. An exothermic reaction has a negative delta H. The H is enthalpy, which is heat of reaction.

An edergonic reaction has a positive delta G. An exergonic reaction has a negative delta G. The G is Gibbs free energy, which is energy available to do work.

A spontaneous reaction has a positive delta S. A non-spontaneous reaction has a negative delta S. The S is entropy (disorder).

Delta means change or difference.

I hope I have been of help.

Once again, wishing you a happy new year 2006.

José