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Homework Help: Heat of Combustion

  1. Mar 30, 2009 #1
    1. The problem statement, all variables and given/known data
    I'm supposed to find the heat of combustion for candle wax (which was used to boil water in a simple calorimeter), yet I have no clue on how to do it, the lab books at school do not tell anything about the calorimeter's specific heat or give a formula for heat of combustion. So far I have my final temperature at 42.0 degrees Celsius, mass of 97.00g (after melting, with base), 1850 cal/g degrees Celsius absorbed by the can (formula used was Cal=mass H2O X Temperature Change H2O X Specific Heat of Water). My mass of H2O was 50g (assuming 1 ml is 1g, unless I got that backwards and its 1mg, I never really understood a few parts of the lab). The mass of my wax is 0.20g (97.20g - 97.00g).

    2. Relevant equations

    All I know is the candle wax's formula, C36H74
    We aren't allowed to take the lab books home, and my data table is brief and straight to the point, the way my teacher wants it to be. I could figure it out on my own if I just get the formula, unless I forget something.
    Last edited: Mar 30, 2009
  2. jcsd
  3. Mar 30, 2009 #2


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    Homework Helper

    First you need to know how much energy you got from the candle.
    For that you need the mass of water (yes 1g=1cc) the specific heat capacity of water and the temperature change (we will ignore the container)

    Be careful of the units - it's probably best to convert everything in kg and J.
    You have the specific heat slightly confused. Water has a specific heat capcity of around 4200J/kg/degree or 1cal/g/degree

    then you can quote the heat of combustion for the candle either in J/kg or since you are given the formula you could work out how many moles and give it as J/mol.
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