Predicting the Spontaneity of 2BH3(g)->B2H6(g): Help Needed!

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Discussion Overview

The discussion revolves around the spontaneity of the reaction 2BH3(g) -> B2H6(g). Participants explore whether the reaction is always spontaneous, always non-spontaneous, sometimes spontaneous, or endothermic, with a focus on the thermodynamic parameters such as entropy (DS) and enthalpy (DH).

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • Some participants note that the entropy change (DSsystem) is negative, indicating a potential challenge in determining spontaneity without additional information on enthalpy (DH).
  • One participant questions whether the reaction can be classified as exothermic simply because it is a synthesis reaction, suggesting that this assumption may not hold without further evidence.
  • Another participant speculates that the reaction may involve borane's electron deficiency leading to dimerization, which could imply a negative change in enthalpy, but acknowledges the difficulty in assessing spontaneity without specific temperature conditions.
  • Some participants express uncertainty about the availability of data during exams, indicating that they may need to rely on reasoning rather than references.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the spontaneity of the reaction, with multiple competing views and uncertainties regarding the thermodynamic parameters involved.

Contextual Notes

Limitations include the lack of access to specific data during exams, dependence on assumptions about enthalpy and entropy, and the unresolved nature of the spontaneity question based on the provided information.

yolo123
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2BH3(g)->B2H6(g)

Which is true?
a) Reaction is always spontaneous.
b) Reaction is always non-spontaneous.
c) Reaction is sometimes spontaneous sometimes not.
d) Reaction is endothermic.
e) Two of the above are true.


I know DSsystem is negative. But I would need more information on DH to say anything else. Please help me!
 
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yolo123 said:
2BH3(g)->B2H6(g)

Which is true?
a) Reaction is always spontaneous.
b) Reaction is always non-spontaneous.
c) Reaction is sometimes spontaneous sometimes not.
d) Reaction is endothermic.
e) Two of the above are true.


I know DSsystem is negative. But I would need more information on DH to say anything else. Please help me!

http://www.nist.gov/data/PDFfiles/jpcrd544.pdf
 
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Chestermiller, we cannot have access to these ressources in exams. We should do it without references. Can we say for sure that the reaction is exothermic since the reaction is a synthesis reaction?
 
yolo123 said:
Chestermiller, we cannot have access to these ressources in exams. We should do it without references. Can we say for sure that the reaction is exothermic since the reaction is a synthesis reaction?
Sorry. I can't help you on this, if that is the case. Please check with Borek who is very knowledgeable.

Chet
 
No idea, which is why I have not commented earlier. Perhaps the data were given in other parts of the test?
 
If this is asked in test, from my experience, you just have to consider that Borane, being electron deficient molecule, tried to remove the deficit by dimerizing (making bond). Hence you could say that the change in Enthalpy is negative. However, it is difficult to say about the spontaneity all by itself, except it can be below certain temperature.

Remember, if this is just a test, my reasoning is a valid flying guess (at least in the type of tests I gave during my college entrance preparations)
 

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