Question about exothermic/endothermic reactions

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Discussion Overview

The discussion revolves around whether exothermic and endothermic reactions can occur in a vacuum, exploring the implications of heat transfer in such conditions. Participants examine specific examples and the nature of energy changes in reactions without surrounding matter.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if exothermic and endothermic reactions can occur in a vacuum and what the implications for heat transfer would be.
  • Another participant suggests that exothermic reactions might emit photons while endothermic reactions require incoming photons.
  • A different viewpoint emphasizes that reactions can result in changes in thermal energy of the products compared to the reactants, using the decomposition of TNT as an example.
  • One participant provides an example of the dissolution of ammonium nitrate in water, explaining that the reaction absorbs energy from the water molecules, resulting in a colder solution.
  • Another example given is the explosive decomposition of nitrogen trichloride, which can occur in a vacuum, indicating that the reaction products can be very hot despite the absence of surrounding matter.
  • A participant raises a question about the feasibility of having reactants in a vacuum, while agreeing that reactions do not necessarily require heat transfer to surroundings.

Areas of Agreement / Disagreement

Participants express differing views on the nature of reactions in a vacuum, with some agreeing that heat transfer to surroundings is not required, while others question the practical implications of reactions occurring without surrounding matter. The discussion remains unresolved regarding the specifics of how reactions behave in a vacuum.

Contextual Notes

Participants do not fully address the implications of having reactants in a vacuum, nor do they clarify the definitions of exothermic and endothermic reactions in this context. There are also unresolved assumptions about the nature of heat transfer in reactions without surroundings.

Alexmer
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I couldn't find the answer to this anywhere so I figured I'd make a thread.

Can exothermic/endothermic reactions occur in a vacuum? Or if there are no surroundings, then what would the transfer of heat be? Thanks.
 
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My guess: exothermic - emit photons. endothermic - needs incoming photons.
 
Or end up with more or less thermal energy in the reaction products than in the initial reagents... That's certainly how I'd expect the (remarkably exothermic) decomposition of TNT to behave.
 
^ Exactly. The energy does not have to come from or go to the surroundings.

Lets use the dissolution of ammonium nitrate as an example of an endothermic reaction. If we put NH4NO3 and water in a thermos bottle or other heat-insulated container, what happens? The ammonium nitrate dissolves and the resulting solution is colder than the water originally was. The energy needed for the reaction has been taken from the vibrational/rotational excitations of the water molecules.

One example of an exothermic reaction is the explosive decomposition of nitrogen trichloride to form nitrogen and chlorine gases: ##2NCl_{3}\longrightarrow N_{2}+3Cl_{2}##. The compound can explode in vacuum just as well as in normal atmosphere, the energy change of 232 kJ/mol in the reaction just means that the reaction products are very hot when they are formed.
 
How can a vacuum contain reactants?

Regardless, the others are right; reactions do not require heat transfer to surroundings.
 
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