Calculating CO2 Released in Propane BBQ Reaction

[rowkem]

I've changed the numbers a bit so things work out a little easier

Homework Statement

The combustion of propane in a BBQ follows the balanced chemical reaction:

C₃H₈ + 5 O₂ ---> 3 CO₂ + 4 H₂O

As this reaction occurs, approximatley 3000J of heat is released. If a roast takes approx. 1500J of heat to cook and only 10% of the heat is actually used to cook the roast, what mass of CO₂ is released into the atmosphere?

Homework Equations

PV=nRT

The Attempt at a Solution

I'm asking this more as a check as to the process I went through, which was as follows:

1) Figured out how much 10% of 3000J was; 300J
2) Re-wrote the equation in terms of 300J:

0.10C₃H₈ + 0.50 O₂ ---> 0.30 CO₂ + 0.40 H₂O

Using that equation figured out how many moles of CO₂ it would take in order to cook the roast: (1500/300)(0.30) = 1.5 moles

Fgured out how many grams of CO₂ that was: ~66g

Compared that to the mass of CO₂ released in the original equation: ~132

Found the difference between the 2 values: 132-66 = ~66g

So 66g of CO₂ is released into the atmosphere...is that correct?

 

[chemisttree]

I got 15 X 44g or 660 grams of CO2.

Does it actually take 1500J to cook the roast or 10% of 1500J? It wasn't clear from the way you phrased the question but I took it to mean that of the Joules of heat produced in the combustion of propane, only 10% are absorbed by the roast. That means you will need 10 X 1500 J to cook the roast.

 

[Blueshift5]

I would like to commend you on your thorough approach to solving this problem. Your calculations and reasoning are correct. However, I would like to point out that the mass of CO2 released into the atmosphere would actually be the same as the mass of CO2 used in the reaction, which is 66g. This is because the conservation of mass states that matter cannot be created or destroyed in a chemical reaction, it can only be converted from one form to another. Therefore, the same amount of CO2 that is used in the reaction to cook the roast is also released into the atmosphere. Keep up the good work!