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Stoichiometry

Discussion in 'DAT Discussions' started by Awuah29, Apr 14, 2007.

  1. Awuah29

    Awuah29 Christian predent 7+ Year Member

    294
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    Oct 13, 2003
    New Jersey
    How many moles of O2 are needed to react with 304.5 g of Cs2 in the combustion reaction below

    Cs2(l) + 3o2 (g)---- Co2(g) + 2 So2 (g)

    the ansewer is 12 mole, but I get 6 moles when I set it up.

    How may grams of H2o will form when 10g of NH3 mixes with 10g of O2 according to the reaction below.

    4 NH3(g) + 5 o2(g)----4 No2(g) + 6 H2o
     
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  3. skyisblue

    skyisblue 2+ Year Member

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    Dec 25, 2006
    Hi Awuah, the answer key is right. It is 12 moles of O2 needed.

    First, convert CS2 to moles and you get 4 moles of CS2. Then, you do a mole ratio of the reactants to get the number of moles of O2.

    4 moles of CS2 x 3 moles of O2/1 mole of CS2 = 12 moles of O2.

    It would help if you capitalize the elements accordingly.
     
  4. Lonely Sol

    Lonely Sol cowgoesmoo fan! 10+ Year Member

    684
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    Dec 13, 2005
    Atlanta, GA
    Is the element, C and S (carbon and sulfur) or is it Cs (Caesium), if it is cesium then there is no way in hell it is 12, but if it C and S2 then it is 12. Yea, skyisblue is right, it must be C and S
     
  5. orthdent786

    orthdent786 Junior Member 5+ Year Member

    71
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    Dec 12, 2005
    for your second question- i think it is a limiting reactant question:

    1. 10 g NH3 X 1 mole NH3/ 17 g NH3 = 0.58 moles NH3
    2. 10 g O2 X 1 mole O2/ 32 g O2 = 0.3125 moles O2

    Since O2 has less moles it is the limiting reactant.

    Therefore;

    0.3125 moles O2 X (6 moles H20/ 7 moles O2) X (18 g H2O/ 1 mole H2O)=

    4.82 g H2O

    I think.. correct me if i'm wrong!

    skyblue your right
    Balanced equation is;

    4NH3 + 7O2 --> 4NO2 + 6H20

    correct?
     
  6. skyisblue

    skyisblue 2+ Year Member

    430
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    Dec 25, 2006
    the 2nd question is a limiting reactant problem, but the equation is not balanced.

    Okay, with the balanced equation, I calculated it to be about 4.78 g of H2O.

    4NH3 + 7O2 to 4NO2 + 6H2O
     
  7. doc toothache

    doc toothache 10+ Year Member

    7,888
    2,052
    Jan 17, 2006
    If it was cesium there would be no SO2, and for that matter no CO2. The only product would be CsO2.
     
  8. gochi

    gochi 10+ Year Member

    1,105
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    Nov 24, 2006
    Correct me if Im wrong, but arent we not allowed to use calculators ?

    How am I suppose to do these difficult calculations w/o a calc ?
     
  9. Nasem

    Nasem 2+ Year Member

    1,009
    0
    Aug 30, 2006
    Lansing, MI
    Relax, I heard the math problems on the DAT aren't highly difficult to compute... Most numbers I hear can be nicly rounded off to
     

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