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Homework Help: Thermochemistry please help

  1. Jan 11, 2007 #1
    Thermochemistry please help!!!!!!!!!!!!!!!!!!

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

    Not sure how to go about this problem.

    Calculate the number of grams of propane (C3H8) required to heat all of the water in a 50-gallon hot-water tank from 23.4 degrees C to 65.0 degrees C if the water tank itself has a heat capacity of 23.4J/ degrees C, and it also uses 2.3 kg of copper pipe.


    2. Relevant equations

    SH of water 4.184kj/g oC

    q= specific heat* mass * change in temp

    3. The attempt at a solution

    Change in temp is 41.6 oC change in H rxn for propane combustion = -2042.804 kj

    tried coverting the kg into grams and the 50 gal into grams and plugged in the info for heat lost by tank = heat gained by water (sh*mass*change in t) =-(sh*mass*change in t). I don't know what to use anymore and how to put the problem together because I keep getting ridiculous answers.
  2. jcsd
  3. Jan 12, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Intially, the water, tank and copper pipes are all at the same temperature : 23.4*C.
    Finally, they all reach the same temperature: 65.0*C

    So first, can you calculate how much heat is required to raise the (water) + (tank) + (pipes) through a temperature difference of 41.6*C?

    Remember to be careful with units; Joule is an SI (or MKS) unit, as is kilogram.
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