<p>So my teacher's not a big fan of answering questions. But I know y'all are.</p>
<p>We did a lab that involved mixing solutions of HCl and NaOH, and trying to find the ∆H associated with the neutralization reaction H+ + OH- --> H2O.</p>
<p>We calculated about 51 kJ/mol. </p>
<p>The next task was to find the theoretical value of ∆H. We reasoned that one bond would be formed, between an oxygen and a hydrogen, and thus found the bond energy of an O-H bond to be 467 kJ/mol.</p>
<p>Whoa, we thought, that's awfully larger. So we looked online and found many places that say the ∆H for the reaction is indeed something like 55 kJ/mol. But none of them have any justification for WHY it wouldn't be the bond energy that would be released when it's formed. (Could it have to do with the charges on the particles?) Do any of you know?</p>
<p>Usually, bond energies are used as approximations for delta H (even still, the approximation is usually pretty close). But in this case, bond energy approximations will not work for 2 reasons: (A) is that the particles are charged and have a high potential energy beforehand that you are not considering and (B) the fact that it is technically H3O+ and OH- makes a difference.</p>
<p>Usually, theoretical delta H is calculated by using a "Thermodynamic Quantities" table in the back of your textbook (appendix usually). You use the standard heats of formation of each of the reactants and products, and delta H = (sum of heats of formation of products) minus (sum of heats of formation of products). This is the theoretical value. The numbers in the table, by the way, have been calculated experimentally under standard thermodynamic conditions (1 atm, 25 degrees C).</p>
<p>According to those calculations:</p>
<p>Hf of H+(aq) = 0
Hf of OH-(aq) = -230
Hf of H2O(l) = -285.83</p>
<p>Calculating (-285.83) - (0 + -230) is indeed around -55.</p>
<p>lol, its funny because it would be faster to look up a good textbook as compared to posting this here. anyway rb9109 is right, the bond energies are simply approximations while the ideal delta H values are found experimentally. </p>
<p>here, let me recommend john mccurry or say kotz, treichel and weaver. i use a cocktail of those two to get most of my non-organic chem reading done.</p>
<p>helllo srrinath and rb9109 thnx…for information pls help in chemistry as im very weak in the subject and im preapring for iit and im losing my score in chemistry…pls help out…</p>