For an experiment I've carried out a series of reactions between monoprotic bases (ammonia and potassium hydroxide) and several acids. Two of these acids were monoprotic (hydrochlori acid and ethanoic acid), another was diprotic (sulfuric acid) and the other was triprotic (phosphoric acid). My results showed that the triprotic acid released more energy per mole than both the diprotic and monoprotic acids, and that the diprotic acid released more energy per mole than the monoprotic acids. This gave rise to my question: how does the proticity of an acid affect the enthalpy change of its reaction with a base?

To be clear I compared my results between weak acids, strong acids so the strength of the acid has already been accounted for.

  • $\begingroup$ I am probably thinking that it has to do with the energy release of the bonds between the H-Cl for example. These most likely release less energy than an H3-PO4 bond. So the distinction here might be due to the number of hydrogen bonds being broken. But I am not quite sure. $\endgroup$ – Brian Blumberg Mar 4 '19 at 2:33
  • $\begingroup$ "per mole" of what? Are you comparing the heat released per proton on the each acid or per mole of acid molecule? $\endgroup$ – Buck Thorn Mar 4 '19 at 10:07

You have to remember that enthalpy change is defined at kilojoules PER MOLE. The concentration won't affect enthalpy change because the same amount of heat is given off per mole of zinc , however the reaction will go faster with a higher concentration.


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