Which reaction will have a negative ∆H value

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SUMMARY

The discussion centers on identifying reactions with a negative ∆H value, indicating that the products are more stable than the reactants. Participants clarify that reactions B and E exhibit negative ∆H due to the stability of their products, while reaction D, which involves ionization, has a positive ∆H value as it requires energy input. The confusion around the definitions of ionization and sublimation is addressed, emphasizing that sublimation (reaction C) also requires energy, thus not qualifying for a negative ∆H.

PREREQUISITES
  • Understanding of thermodynamics, specifically enthalpy changes (∆H)
  • Knowledge of chemical stability and molecular structures
  • Familiarity with reaction types, including ionization and sublimation
  • Basic principles of energy requirements in phase changes
NEXT STEPS
  • Research the concept of enthalpy and its implications in chemical reactions
  • Study the stability of molecular structures and their relation to enthalpy changes
  • Explore the differences between ionization and sublimation processes
  • Investigate the energy requirements for dissociation of diatomic molecules
USEFUL FOR

Chemistry students, educators, and anyone studying thermodynamics and reaction energetics will benefit from this discussion.

TT0
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Homework Statement


Screen Shot 2016-07-04 at 2.14.39 PM.png

Homework Equations

The Attempt at a Solution


Negative ∆H means that the product is more stable. Change from solid to gas requires energy so cancel out A and C. Reaction D doesn't make sense. The products of reaction B and E are more stable than the reactant because there is a full shell so it seems to me both would have a ∆H value. Can someone tell me what am I missing?

Cheers!
 
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Reaction D does make a perfect sense.

Ionization always requires energy.
 
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I thought chlorine didn't monatomic gases. So are you saying D is the answer? If so, why does it release energy?

Thanks a lot
 
TT0 said:
I thought chlorine didn't monatomic gases.

Every diatomic molecule can be split (forced to dissociation) at temperatures high enough. It typically requires a lot of energy (hence the need for high temperatures).
 
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I see, so D has a positive ∆H value.

Would you say both B and E have negative ∆H as the products are more stable?

Cheers!
 
TT0 said:
Would you say both B and E have negative ∆H as the products are more stable?
Borek said:
Ionization always requires energy.
 
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So I guess A is the answer then? As it does not ionise. C is sublimation which requires energy. If A is the answer, isn't energy required for a particle to turn into a gas?

Thanks!
 
E is not ionization.
 
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I see. I got confused and forgot ionisation does not mean turning into an ion. Thanks a lot
 

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