Calculating Standard Molar Enthalpy of Formation at 298K for N2O5 (g)

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Discussion Overview

The discussion revolves around calculating the standard molar enthalpy of formation for N2O5 (g) at 298 K, specifically how to relate the given standard molar internal energy of formation to enthalpy under certain conditions. The scope includes thermochemistry concepts and problem-solving strategies.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant states the standard molar internal energy of formation of N2O5 (g) is 17.433 KJ/mol at 298 K and seeks guidance on calculating the standard molar enthalpy of formation.
  • Another participant explains the relationship between enthalpy (delta H) and internal energy (delta U), suggesting the equation delta H = delta U + P delta V, and questions how to approach the problem under constant volume conditions.
  • A different participant posits that if the volume is constant, then delta H would equal delta E.
  • One participant expresses frustration with the professor's assignment of problems that do not align with class material, questioning the relevance of the 298 K specification.
  • Another participant clarifies that while temperature is often specified in thermochemistry questions, it is not necessary for calculating the answer, and suggests that the professor may be trying to encourage independent research.
  • The original poster expresses gratitude for the help but notes that the relevant material is not covered in their textbook, indicating a gap in the resources provided for the course.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of the temperature specification and the relevance of the problem to the course material. There is no consensus on how to approach the calculation under the given conditions.

Contextual Notes

Participants mention the lack of information regarding pressure and volume in the problem statement, which may affect the calculation of enthalpy. The discussion also highlights potential gaps in the textbook material related to the topic.

ace123
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This is my last thermochemistry question.

The standard molar internal energy of formation of N2O5 (g) is 17.433 KJ/mol at 298 K. What is the standard molar enthalpy of formation of N2O5 (g) at the same temperature.

I just need hint, like what do i do with the 298K?
 
Last edited:
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its delta H = delta U (E) + P delta V

molar internal is delta E and if you had data for P and delta V, you could get delta H (enthalpy). But what if this is done at CONSTANT volume, what happens to P delta V (your question doesn't give this condition but it also doesn't give P or delta V values - it might be leading you this way)? how can you find delta H under this constant volume condition?
 
Well if volume is kept constant then the delta H will be just E?
 
Yes, correct,

and NO, I'm not stalking you, just trying to help out where I can - solving chem problems is fun for me and you seem to have some fun problems :smile:
 
Only reason they are fun is because my professor gets them from some website and doesn't even check to see if they relate to what we have done in class. Which is why I'am forced to ask for help :smile:

Edit: So why even give the 298K. Just to tell us that it's not standard pressure?
 
I think you mean standard state but no, the temp is not necessary to get the answer. However, temp is often specified as well in these thermochem questions but not part of the standard states (1atm and 1M). Might as well be though,

Your prof is trying to get through some material without lecturing about it in class (might be because he is behind in his schedule) and so is trying to get you to go look this up (or ask for help ... :) ) and read other parts of your textbook, there must be another part of the chapter on thermochem that deals with total energy of a reaction, which is what I should have suggested that you go do in the first place... ;)

enough fun for me, I've got to go back and do my own work...
 
Last edited:
Well thanks for your help and I won't bother you again. Well at least for today. Unfortunately this really isn't in my textbook. Only part that deals with energy. Also my chem class is a lecture so is supposed to lecture about it :)
 

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