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    Hi, don't quite understand how this works for these questions.

    1.How many atoms are in 0.25 moles of O2 at STP.

    I got the answer as 0.25 x Av constant which is 1.5x10^23, but the answer is 3.01x10^23 which is half of Av constant not 1/4 which doesnt seem to make much sense to me.

    2. How many litres are in 56 grams of N2 at STP.

    1 Mole of a gas has 22.4L and here there are 4 moles so won't it be 89.6, but the answer is 44.8L. Once again, don't understand how they got this answer.

    Really Appreciate the help!
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    (Original post by ChemBoy1)
    Hi, don't quite understand how this works for these questions.

    1.How many atoms are in 0.25 moles of O2 at STP.

    I got the answer as 0.25 x Av constant which is 1.5x10^23, but the answer is 3.01x10^23 which is half of Av constant not 1/4 which doesnt seem to make much sense to me.

    2. How many litres are in 56 grams of N2 at STP.

    1 Mole of a gas has 22.4L and here there are 4 moles so won't it be 89.6, but the answer is 44.8L. Once again, don't understand how they got this answer.

    Really Appreciate the help!
    For question 1:
    There are two atoms of oxygen in a molecule.
    This means there are 0.5 moles of oxygen atoms.
    Hence 0.5*6.02x10^23=3.01x10^23
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    Hi, sorry didn't quite understand that 0.5 moles part, could you explain that please. Thanks!
    (Original post by danielwinstanley)
    For question 1:
    There are two atoms of oxygen in a molecule.
    This means there are 0.5 moles of oxygen atoms.
    Hence 0.5*6.02x10^23=3.01x10^23
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    (Original post by ChemBoy1)
    Hi, sorry didn't quite understand that 0.5 moles part, could you explain that please. Thanks!
    Sure..

    so there are 0.25 moles of oxygen molecules
    A mole is just an amount of substance
    So 2*0.25 = 0.5
    so there are 0.5 moles of oxygen atoms
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    For question 2:

    If we use Number of moles = mass/molar mass
    Molar mass = 14+14
    you get 56/24.0 = 2.00 moles

    So there are 2 moles.
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    Thanks, that really helps!
    (Original post by danielwinstanley)
    For question 2:

    If we use Number of moles = mass/molar mass
    Molar mass = 14+14
    you get 56/24.0 = 2.00 moles

    So there are 2 moles.
 
 
 
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