Calculate Qv from Qp: deltaH and deltaU

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SUMMARY

The discussion centers on the calculation of Qv from Qp using the relationships Qp = deltaH and Qv = deltaU. It establishes that deltaH can be expressed as deltaU plus the term deltanRT, leading to the equation Qv = deltaH - deltanRT. The user calculated Qv as -2001.42 kJ/mol, but faced discrepancies in their online assignment, prompting a request for algebra verification and clarification on Δn, the change in the number of moles of gas.

PREREQUISITES
  • Understanding of thermodynamic concepts such as enthalpy (deltaH) and internal energy (deltaU).
  • Familiarity with the ideal gas law and the significance of the change in number of moles (Δn).
  • Basic algebra skills for manipulating thermodynamic equations.
  • Knowledge of the gas constant (R) and its units, specifically 8.3145 x 10^-3 J/K·mol.
NEXT STEPS
  • Review the derivation of the relationship between deltaH and deltaU in thermodynamics.
  • Study the implications of Δn in gas reactions and its effect on energy calculations.
  • Practice solving thermodynamic equations involving enthalpy and internal energy changes.
  • Explore common pitfalls in thermodynamic calculations to avoid errors in online assignments.
USEFUL FOR

Students in chemistry or thermodynamics courses, educators teaching thermodynamic principles, and anyone involved in energy calculations in chemical reactions.

aruhland
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Homework Statement
For the reaction below, constant pressure heat of reaction is Qp=-2051 kj/mol at 25 C. What is the constant volume heat of reaction, Qv, at 25 C?

10CO(g) + 21H2(g) --> C10H22(l) + 10 H2O(l)
Relevant Equations
enthalpy change=internal energy change + change in mol=*R*T
internal energy change=Qv-Pext*volume change
Qp=deltaH
Qv=deltaU
deltaH=deltaU + deltanRT
Qv=deltaH - deltanRT
=-2051 kj/mol - (11mol-31mol)(8.3145x10-3J/Kmol)(298.15K)
=-2001.42 kJ/mol

I thought I did this correctly but it comes up as wrong for my online assignment. Any suggestions?

deltaH=enthalpy change
deltaU=internal energy change
 
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Check your algebra
 
What is Δn? Change in number of moles of gas...
 
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