Constant Volume Heat of Combustion from heat capacity of calorimeter

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Discussion Overview

The discussion revolves around calculating the constant volume heat of combustion using the heat capacity of a calorimeter. Participants are examining the formula used and the implications of their calculations, including unit considerations.

Discussion Character

  • Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • One participant presents a calculation for the heat of combustion but acknowledges that the answer is incorrect and questions the units used.
  • Another participant raises the point that heat of combustion is typically expressed as a positive value, suggesting a potential misunderstanding in the sign of the calculated result.
  • A third participant references the equation Q=nCdeltaT, prompting questions about the meaning of the terms and their units, and challenges the correctness of the initial calculation.
  • A later reply expresses realization of a mistake, indicating a moment of reflection on the previous contributions.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the correctness of the calculations or the interpretation of the heat of combustion values. Multiple competing views regarding the sign of the heat of combustion and the calculation process remain evident.

Contextual Notes

There are unresolved questions regarding the definitions of terms in the equation and the proper handling of units in the calculations. The discussion does not clarify these aspects fully.

Who May Find This Useful

Students or individuals interested in thermodynamics, calorimetry, and the principles of heat transfer may find this discussion relevant.

aruhland
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Homework Statement
A 0.009089 mol sample of an organic compound was burned in oxygen in a bomb calorimeter. The temperature of the calorimeter increased from 24.3 C to 31.1 C. If the heat capacity of the calorimeter is 4.38 kj/C, what is the constant volume heat of combustion of this compound, in kj/mol?
Relevant Equations
Qcal=heat capacity calorimeter * change in temperature
Q=nCdeltaT
Qcal=-Qrxn
Q=heat capacity calorimeter*(-)change in T*moles
=0.009089mol*-6.8C*4.38kj/C
=-0.2707kj/mol

This answer is wrong but it was the only one I could come up with right now. I just noticed units in the answer would be wrong too. Any suggestions?
 
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Isn't heat of combustion given as a positive value?
 
aruhland said:
Q=nCdeltaT
What do the terms in this equation mean? What are their units? Have you done your calculation correctly?
 
Oh my, how I missed that :(
 

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