Energy changes and rates of reaction

[allanwinters]

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.

 

[DrClaude]

Don't you also need an equation for the partial burning leading to the formation of CO?

 

[DrClaude]

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

 

[Mastermind01]

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.

 

[DrClaude]

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

 

[Mastermind01]

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

Can you please explain?

 

[DrClaude]

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.

 

[Mastermind01]

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

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