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Homework Help: Bunch of Equations and Stoichiometry

  1. Oct 18, 2005 #1
    I'm totally stuck; please if you could get any of these solved so that i can go ahead with the hints and help myself out... It's tragic!
    -A cube of redwood 3.00 cm on an edge weighs 11.8 g. What's its density?
    -A beaker containing 4.00 x 10^2 cm^3 of a liquid having a density of 1.85 gcm^3 is found to weigh 884 g. What is the mass of the empty beaker?
    -4.90 kg of water is heated from 15 to 48 degrees celcius. How much heat is absorbed by the water? In Kilocalories/Kjoles?
    -A sample with 7.5x10^21 molecules of Cyclohexane contains 4.5x10^21 carbon atoms and 9.0x10^21 hydrogen atoms. Empirical/Molecular formulae?
    -How many moles of Hydrogen atoms are necessary to combine with 7.0x10^-4 mol of Nitrogen atoms to form the compound Ammonia?
    -Given eight atoms of Oxygen; how many molecules of the compounds N20, NO, CO2, N204, (any you prefer...) are possible to make?
  2. jcsd
  3. Oct 18, 2005 #2


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    You need to show that you have made some attempt at your questions, so we can see where you are getting stuck..

    I can get you started on the first one. Do you know the general equation for density (related to mass and volume)?
    You need to be aware that different measuring systems will yield different answers. Be consistent with your terms (you may need to convert some so they will be in the same measuring system). Your first example is in the cgs system. You are lucky, all the terms are in the same system. Don't assume this will always be the case.

    The second question is a little bit more challenging. If you know the formula for density, you should be able to find the mass of the liquid and subtract it from the total mass measured.
  4. Oct 18, 2005 #3


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    As for...

    3) There is a formula for E that relates to the specific heat of a substance. This will help you determine the answer
    4) That is just too simple, its very straight forward.
    5) First, write out the equation then use the ratios to determine how many hydrogen atoms are necessary
    6) Obvious.
  5. Oct 20, 2005 #4
    That was helpful! Thanks.
    I thought maybe i could use some hints with 6 and 4...?
  6. Oct 20, 2005 #5


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    You are given: have 8 atoms of Oxygen.

    In the first compound N20 how many Oxygen's are needed per molecule? (one)
    How many of that type of molecule can you make? 8/1 = 8

    For the third molecule CO2, how many Oxygen's are needed? (two)
    How many of that type can you make? 8/2 = 4

    Use a similar thought process for the other molecules.
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