Energy changes and rates of reaction

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Discussion Overview

The discussion revolves around the calculation of carbon monoxide emissions from the combustion of methane, specifically addressing the mass of CO produced when burning 100g of natural gas. Participants explore the implications of energy changes and the rates of reaction in this context, with a focus on both complete and partial combustion processes.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents a calculation method involving the conversion of 100g of methane to moles and using the standard molar enthalpy of formation to find energy produced, leading to a mass of CO emissions.
  • Another participant questions the need for an equation for partial burning that leads to CO formation.
  • Concerns are raised about the units used in the emission factor (19.14kg/MJ) and the resulting mass of CO being produced from 100g of methane.
  • Some participants suggest that the energy produced from burning 100g of methane should be used directly to calculate CO emissions, rather than involving additional reactions.
  • There is a discussion about the significance of CO production and whether it can be neglected in the calculations, with some participants agreeing that it should be considered if the emission level is significant.
  • One participant acknowledges that their method yields the textbook answer but admits it may be technically incorrect.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of considering partial combustion and the implications of the emission factor. There is no clear consensus on the correct approach to the problem, and multiple competing views remain throughout the discussion.

Contextual Notes

Participants highlight potential limitations in the assumptions made regarding the combustion process and the energy values used, as well as the dependence on the definitions of complete versus partial combustion.

allanwinters
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Homework Statement


The complete combustion of methane is represented in the following equation:
CH4(g) + 2O2 -> CO2(g) +2H2O(g) +802.5 kJ
Assume that natural gas is essentially methane. The emission level of Carbon monoxide, CO(g) from the burning of natural gas is 19.14kg/MJ of energy produced.

Homework Equations


What mass of CO(g) will be emitted when 100g of natural gas is burned?

The Attempt at a Solution


I attempted to convert the 100g of methane into mol (100g/16.04g per mol) and then i multiplied the mol by it's standard molar enthalpy of formation on wikipedia (-74.9KJ/mol) to find the KJ then converted it into MJ and multiplied the methane mol with 19.14Kg/MJ. My answer was wrong. The textbook answer is 95.7 kg.
 
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Don't you also need an equation for the partial burning leading to the formation of CO?
 
The units seem to be off. 19.14kg/MJ doesn't make sense, as well as producing 95.7 kg of CO when burning 100 g of methane :confused:
 
You're complicating it. 802.5 kJ (I think you've got the sign wrong) is the energy produced from the burning of natural gas. Just calculate the total energy produced for 100 g of methane and use the total energy to find amount of CO emission.
 
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Mastermind01 said:
You're complicating it. 802.5 kJ (I think you've got the sign wrong) is the energy produced from the burning of natural gas. Just calculate the total energy produced for 100 g of methane and use the total energy to find amount of CO emission.
I agree that this can be done instead of my suggestion of using a second reaction, if the production of CO is negligible. But not if it is 19.14kg/MJ :smile:
 
DrClaude said:
I agree that this can be done instead of my suggestion of using a second reaction, if the production of CO is negligible. But not if it is 19.14kg/MJ :smile:

Can you please explain?
 
Mastermind01 said:
Can you please explain?
If the production of CO is important, then you can't simply take that combustion of 1 mole of CH4 will release 802.5 kJ. You have to weigh that value with the energy produced by the reaction leading to CO, which releases less energy than the complete combustion.
 
DrClaude said:
If the production of CO is important, then you can't simply take that combustion of 1 mole of CH4 will release 802.5 kJ. You have to weigh that value with the energy produced by the reaction leading to CO, which releases less energy than the complete combustion.

Aah, I see your point. Thanks :smile:

Anyway, my method does get the OP's textbook answer even though it's technically incorrect.
 

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