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Homework Help: Gas laws problem (need quick help )

  1. Sep 25, 2008 #1
    gas laws problem (need quick help plz)

    1. The problem statement, all variables and given/known data
    ill try to describe the situation as best i can
    at first we have a flask (150 ml) with 0.1g of NaHCO3 we attach a syringe with 20ml of acetic acid (CH3COOH ) to it (and seal it off so nothing escapes)
    we inject the acetic acid into the flask and pull the syringe back (so the overall volume doesnt change) the 2 compounds react and produce CO2
    the initial(before adding the acetic acid) temp. = 295.6k
    initial pressure = 1.020 atm
    final temp. = 297.6 k
    final pressure = 1.176
    what is the initial amount of gas in the flask(in mol)?
    and what is the amount of co2 added(in mols)?
    what is the partial pressure of CO2

    2. Relevant equations
    ideal gas law equations

    3. The attempt at a solution
    i used pv=nrt to calculate the initial amount of gas (using the initial conditions) = 6.45*10-3 mol
    for the second part i use PV/nT(initial)=PV/nT(final) to get the amount of mols after the reaction but i get a value less than the first one. this doesnt make sense since we are adding gas to it (note that this was a real experiment and the values might be off from an ideal situation)
    can someone help me out with this and maybe hint at what to do on the last 2 parts ?

    i really appreciate the help
  2. jcsd
  3. Sep 26, 2008 #2


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    Staff: Mentor

    Re: gas laws problem (need quick help plz)

    Use PV=nRT for he second part as well. PV/nT=const holds only for constant n.
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