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Heat of Reaction Experiment, High school level

  1. Jun 30, 2007 #1
    The problem statement, all variables and given/known data
    I am working on a correspondence grade 12 Chemistry Course and I am confused by one question. I did an experiment involving hydrochloric acid (HCl) and sodium hydroxide (NaOH). Here is the question:
    "In a reaction, Na+ ions are separated from OH- ions, a process of dissociation that absorbs energy, yet, in the end, heat was liberated by the overall process. Explain."

    This has been asked before on this forum but there was not really a clear answer posted so I thought perhaps we could discuss it again. Here is the archived thread: https://www.physicsforums.com/archive/index.php/t-77030.html

    The attempt at a solution
    So I understand that, since the reaction was exothermic, something other than the breaking of the NaOH bonds must have occurred which took less energy and thus released the excess energy in the form of heat. I do not quite understand what happened that would have taken so much less energy. Would the following be a correct and reasonable answer: "The reorganization and formation of water took much less energy and resulted in heat being released." ?
  2. jcsd
  3. Jun 30, 2007 #2


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    The solvated proton from the acid and the solvated hydroxide from the base are less stable (and have the potential to react...) than the water which results from their combining. The water is more stable than the separate ions. Energy is released into the environment upon this neutralization, and the increase in temperature can be observed (and measured).
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