1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Figuring out the amount of CO2 that goes into the atmosphere when cooking a roast

  1. Oct 7, 2009 #1
    I've changed the numbers a bit so things work out a little easier

    1. The problem statement, all variables and given/known data

    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?

    2. Relevant equations


    3. 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?
  2. jcsd
  3. Oct 14, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Re: Figuring out the amount of CO2 that goes into the atmosphere when cooking a roast

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook