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Homework Help: Chemistry Homework

  1. Oct 20, 2007 #1
    2H2+O2=2H2O+242kJ (HEAT)
    -How many grams of H2 gas are required to produce 2.21x103 kJ of heat?
    -How many grams of H2 gas are required to react with 785 gm of O2 gas?
    -If 300 gms of O2 gas and 75 gms of H2 gas are mixed and burned what is the limiting reactant?
    -How many grams of H2O are produced in question above?

    please help
  2. jcsd
  3. Oct 20, 2007 #2


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    Staff Emeritus
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    Welcome to the forums. Please note that you are required to show working before we can help you. So, do you have any thoughts?
  4. Oct 26, 2007 #3

    i have no idea
  5. Oct 26, 2007 #4


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    Remember that everything in a chemical equation is a ratio, including energy.

    If 2 moles of H2 gives you 242kJ, what mass of H2 gives you 242kJ? Now what mass of H2 do you need for your desired amount of energy?
  6. Oct 26, 2007 #5
    do i multiply H2 mass by 2210? is 2 the mass of H2?
  7. Oct 26, 2007 #6
    Yes the mass of H2 is 2, don't you have a periodic table of elements? What TMM was trying to say is that if you have 2 moles of H2 that gives 242 KJ. How many moles would give you 2.21x103 kJ. It's just a simple ratio
  8. Oct 26, 2007 #7
    thank u, TMM and ace123
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