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Homework Help: Chemical Energetics

  1. Aug 16, 2007 #1
    1. The problem statement, all variables and given/known data
    The standard enthalpy change of combustion of propane (C3H8)
    is -2220kJ/mol. It requires 1.0J of energy to raise the temperature of 1.0g of air by 1.0K.

    Calculate what mass of propane needs to be burned to raise the temperature of the air in the balloon by 50K.

    2. Relevant equations

    3. The attempt at a solution

    For the air in balloon to raise by 50K,50J is needed I suppose.
    50/(mass of propane/44.0)=2220x10^3
    mass of propane = 9.91x10^(-4)g
    The answer given is (1.85x10^3)g.
    Can anyone correct me?
  2. jcsd
  3. Aug 16, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    You need to know the mass of air in the balloon or it's initial volume / temperature / pressure.
    Otherwise your answer is correct per g of air.
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