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Homework Help: Chemistry Homework- Stoichiometry: Volume and Particle Calculations

  1. Jan 10, 2009 #1
    Chemistry Homework-- Stoichiometry: Volume and Particle Calculations

    This is only to check my work, and I may be updating this post with more problems. There are ten questions total, and this is NOT graded. Therefore, the help I recieve goes toward my understanding, not my score.

    1. The problem statement, all variables and given/known data
    What VOLUME of oxygen is produced from the decomposition of 5.67 x 10^24 molecules of water?
    Balanced equation:
    2H2O >decomposes to> 2H2 + O2

    2. Relevant equations
    6.02 x 10^23 molecules : 22.4L @STP for any gas
    Mol-Mol ratio = 1 mol O2/ 2 mol H2O

    3. The attempt at a solution
    Trying to go along with dimensional analysis format.
    (5.67 x 10^24)/(6.02 x 10^23) x 1 mol O2/ 2 mol H2O x 22.4L = 105.488L

    Is the mol-mol ratio necessary? Without it, the answer comes out to 210.977L (rounded).
  2. jcsd
  3. Jan 10, 2009 #2


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    Homework Helper
    Gold Member

    Re: Chemistry Homework-- Stoichiometry: Volume and Particle Calculations

    Your answer is correct, or more cautiously, I get the same.
    Why are you insecure?
    A mole of gas occupies i.e. 6.02 x 1023 molecules of gas, occupies 22.4 l at standard atmospheric pressure and temperature.
    Independently of how many atoms are in each molecule.
    I.e. 6.02 x 1023 molecules of gas occupies 22.4 l under standard conditions - however many atoms there are in each molecule.

    6.02 x 1023 molecules of Argon (A), 6.02 x 1023 molecules of oxygen (O2) or 6.02 x 1023molecules of ethane (C2H6) all occupy 22.4 l even though this is 6.02 x 1023 atoms of A, 2X6.02 x 1023 atoms of O2, or 8X6.02 x1023 atoms of ethane .

    The rough basic reason for that is that any gas at a given pressure and temperature has the same average kinetic energy in the translational movement of the molecules. If it didn't then say you had a balloon of argon surrounded by oxygen at the same pressure then the argon atoms bounding of the inside of the balloon would transfer different momentum to it outwards than the oxygen atoms bouncing would transfer inwards. The baloon would expand or contract, in fact the pressure could not have been the same outside and inside to start with. I am not saying that is quite obvious, but that is what is shown in kinetic theory somewhere in your textbooks or maybe someone could explain better here.
    Last edited: Jan 10, 2009
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