Calculate Heat of Combustion of Graphite

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Discussion Overview

The discussion revolves around calculating the heat of combustion of graphite when combusted incompletely, specifically focusing on the generation of carbon monoxide (CO) and carbon dioxide (CO2). Participants are attempting to determine the correct heat released based on the combustion reactions and the stoichiometry involved.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant states the heat of combustion for graphite and CO, suggesting a calculation based on these values.
  • Another participant questions the initial calculations, prompting a reevaluation of the moles of carbon burned and the gaseous products formed.
  • Participants agree that 1 mole of carbon is combusted, producing 0.5 moles of CO and 0.5 moles of CO2.
  • There is a calculation presented for the heat released based on the combustion reactions, leading to a proposed total of -535.5 kJ/mol.
  • One participant suggests calculating the heat for half a mole of CO, leading to a value of 197 kJ/mol, but there is confusion regarding the total heat released based on the stoichiometry of the reactions.

Areas of Agreement / Disagreement

Participants generally agree on the stoichiometry of the combustion reactions but disagree on the calculation of the total heat released, leading to multiple interpretations of the results.

Contextual Notes

There are unresolved aspects regarding the assumptions made in the calculations, particularly concerning the heat values used and the interpretation of the combustion process.

Hamal_Arietis
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Homework Statement


The heat of combustion of graphite and that of CO is 394kJ/mol and 283 kJ/mol, respectively. When 12g of graphite is combusted incompletely, the same volume of CO and CO2 are generated. Calculate the heat of generated by this combustion. Choose the closet value.(kJ)
A.197 B.253 C.308 D.339 E.505 F.677

Homework Equations


The answer is B.253kJ

The Attempt at a Solution


My idea is:
##C+O2→CO\\
1 \qquad \qquad 1## and ##ΔH_1=-394kJ/mol##
##CO+O2→CO2\\
0,5 \qquad \qquad 0,5## and ##ΔH_2=-0,5.283 kJ/mol##
So ##ΔH=ΔH_1+ΔH_2=-535,5kJ/mol##
Where is my wrong?
Thanks for helping
 
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Hamal_Arietis said:
Where are my wrong?
Hamal_Arietis said:
The answer is B.253kJ
Wrong.
Ask yourself, "How many moles of carbon have been burned? How many moles of gaseous products have been formed? What is the minimum heat?"
 
Bystander said:
How many moles of gaseous products have been formed?
I think 0,5 mol CO and 0,5 mol CO2 are generated and 1 mol C is combusted
 
Hamal_Arietis said:
I think 0,5 mol CO and 0,5 mol CO2 are generated and 1 mol C is combusted
Correct. And the minimum heat released is what?
 
Bystander said:
Correct. And the minimum heat released is what?
I don't know.
##C+O2→CO\\
1 \qquad \qquad 1## and ##ΔH_1=-394kJ/mol##
##CO+O2→CO2\\
0,5 \qquad \qquad 0,5## and ##ΔH_2=-0,5.283 kJ/mol##
So ##ΔH=ΔH_1+ΔH_2=-535,5kJ/mol##
1 mol of C is combusted and 0,5 mol of CO and CO2 are generated . So the heat is -535,5kJ/mol?
 
What's half a mol x 394 kJ/mol?
 
Bystander said:
What's half a mol x 394 kJ/mol?
197kJ/mol
but 1 mol C is burned, not 0,5 mol. And 1mol CO is generated but 0,5 mol CO is burned and 0,5 mol CO2 is generated.
 
Yes, and ...
 

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