Chemistry

posted by Heather

The amount of energy released by burning a fuel source, measured in energy per mass, is called the fuel value. If all the energy obtained from burning 1.28 pounds of methane (fuel value is 11.97 kcal/g) is used to heat 127.0 kg of water at an initial temperature of 21.5 °C, what is the final temperature? help??

  1. DrBob222

    1.28 lbs x 453.59 g/lb = ?grams CH4.
    ?grams CH4 x (11.97 cal/g) = ? cal heat produced by the l.28 lbs CH4.

    ?cal = mass H2O x specific heat H2O x (Tfinal-Tintial)
    Substitute 127,000 for mass H2O
    Solve for Tf
    Substitute 21.5 for Ti
    Substitute 1 cal/g for specific heat H2O.

  2. Heather

    I keep getting the wrong answer :/
    I did:
    1.28lb x 453.59g/lb= 580.5952g CH4
    580.5952g Ch4 x 11.97 cal/g= 6949.724544 cal
    6964.724544 cal= 127,000 x 1 cal/g x (Tf-21.5)
    Final Temp= 21.6*C
    but this answer was wrong

  3. Heather

    nvm! i got it! I forgot to convert 11.97 kcal/g to cal/g

  4. DrBob222

    1.28lb x 453.59g/lb= 580.5952g CH4
    580.5952g Ch4 x 11.97 cal/g= 6949.724544 cal
    6964.724544 cal= 127,000 x 1 cal/g x (Tf-21.5)
    You are ok to here. You didn't show your next step but that is the error. Here is your last line.
    6964.72 = 127 x 1 x (Tf-21.5)
    Then
    6964.72 = 127Tf - (127*1*21.5)
    6964.72 = 127Tf - 2730.50
    6964.72 + 2730.50 = 127Tf
    I'll let you take it from here.
    Final Temp= 21.6*C

  5. DrBob222

    I forgot and didn't turn off the bold and it printed hat last line in bold. Ignore "Final Temp = 21.6"

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