Is this exothermic reaction truly endoenergetic?

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Discussion Overview

The discussion revolves around the classification of a chemical reaction involving iodine and hydrogen, specifically whether it is truly exothermic or endoenergetic based on bond energies and enthalpy changes. Participants analyze the energy dynamics of bond breaking and formation in the context of thermodynamics.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant argues that if the energy required to break the bonds in H2 and I2 exceeds the energy released in forming HI, then the reaction should be classified as endoenergetic, contradicting the exothermic classification.
  • Another participant states that a negative enthalpy change indicates an exothermic reaction, suggesting that the energy associated with bonds being formed is greater than that of the bonds being broken.
  • A later reply provides specific bond enthalpy values, calculating the enthalpy change for the reaction and supporting the claim of an exothermic reaction.
  • One participant expresses agreement with the calculations and suggests a possible typo in the reference book regarding the classification of the reaction.

Areas of Agreement / Disagreement

Participants express disagreement regarding the classification of the reaction as exothermic or endoenergetic, with some supporting the exothermic classification based on enthalpy calculations, while others maintain that the initial interpretation of bond energies suggests an endoenergetic process.

Contextual Notes

The discussion includes varying interpretations of bond enthalpies and their implications for the reaction's enthalpy change. There is also a mention of potential typographical errors in reference materials, which may affect the understanding of the reaction's classification.

PPonte
I2 (g) + H2 --> 2HI dH = - 10 kJ/mol

In this reaction the energy involved in the breaking of bonds in H2 and I2 is great in quantity than the energy released in the formation of bonds in HI.


My book says that this sentence is true, but I do not agree.
The breaking of bonds is an endoenergetic process and the formation of bonds is an exoenergetic process. If the reaction is exoenergetic this means that the exoenergetic process involves more energy than the endoenergetic process.
We can see it by other way. If the energy involved in the breaking of bonds in H2 and I2 is great in quantity than the energy released in the formation of bonds in HI this means that the reactional systhem obtained energy and thus the enthalpy of the products is higher than the enthalpy of the reactants, which is an caractheristic of an endoenergetic reaction and not of an exoenergetic reaction.
Am I right?
 
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If the enthalpy change is negative, this indicated an exothermic reaction, energy is being release into the surroundinga. The energy associated with bonds being made is greater than that of the bonds being broken.
 
Exactly! I think I am right.
 
According to my data the bond enthalpies are as follows:
[tex]H-H = 436 kJ\cdot mol^{-1}[/tex]
[tex]I-I = 151 kJ\cdot mol^{-1}[/tex]
[tex]H-I = 298 kJ\cdot mol^{-1}[/tex]
This gives the enthalpy of broken bonds to be 587 and bonds made of 596 which means:
[tex]\Delta H = -9 kJ\cdot mol^{-1}[/tex]
Which would agree with your comments. It seems your book has a typo!
 
It seems so. But has less typos than the other books I had.
Thank you very much for your help!
 

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