Constant Volume Heat of Combustion from heat capacity of calorimeter

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SUMMARY

The discussion centers on the calculation of the constant volume heat of combustion using the heat capacity of a calorimeter. The formula presented is Q = heat capacity calorimeter * (-)change in T * moles, leading to a calculated value of -0.2707 kJ/mol. Participants highlight the incorrectness of the answer due to unit discrepancies and the expectation that the heat of combustion should be expressed as a positive value. Clarification on the terms and units involved in the calculation is sought.

PREREQUISITES
  • Understanding of calorimetry principles
  • Familiarity with heat capacity concepts
  • Knowledge of thermodynamic equations
  • Basic proficiency in unit conversion and dimensional analysis
NEXT STEPS
  • Review the principles of calorimetry and its applications in thermodynamics
  • Study the correct usage of the equation Q = nCΔT in heat calculations
  • Learn about the significance of sign conventions in thermodynamic processes
  • Explore the concept of heat of combustion and its measurement techniques
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Chemistry students, thermodynamics researchers, and professionals involved in calorimetry and combustion analysis will benefit from this discussion.

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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