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    Hey guys.... do we need to know any of the half equations in the hydrogen fuel cell?
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    (Original post by lifeisgood2012)
    Hey guys.... do we need to know any of the half equations in the hydrogen fuel cell?
    Yeah pretty sure we do. I remember them as...
    2H2 -----> 4H+ + 4e-
    O2 + 4H+ + 4e- -------> 2H2O

    which will balance out to give...2H2 + O2 -----> 2H2O
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    Does anyone have the advantages/disadvantages associated with the use of the different electrochemical cells?

    Are we meant to do non-rechargeable vs rechargeable vs fuel cells or for each individual cell?
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    (Original post by samfreak)
    if u worked out the temperature T from the gibbs free energy change, and the reaction was exothermic, what would be the range of temperature that the reaction would be feasible for? is it <t or >t ?

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    go from the formula as normal:

    eg feasible when deltaH - TdeltaS < 0

    just remember that when you divide by a negative number, you reverse the inequality sign..
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    (Original post by lifeisgood2012)
    Hey guys.... do we need to know any of the half equations in the hydrogen fuel cell?
    (Original post by Gazfink)
    Yeah pretty sure we do. I remember them as...
    2H2 -----> 4H+ + 4e-
    O2 + 4H+ + 4e- -------> 2H2O

    which will balance out to give...2H2 + O2 -----> 2H2O
    what he said is in acidic conditions.
    the other ones you need to know are;
    4e- + 2H2O + O2 ---> 4OH-
    4e- + 4H2O ---> 4OH- + 2H2

    (both written as reductions)

    sum of both equations is the same overall as in acidic conditions
    2H2+O2--->2H2O. same cell emf.
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    guys do we need to know any half equations for the titration calculation question thats gone come up?
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    I got an a overall for as. Howver I am looking to get an a*. In unit 4 I got 108ums which is exactly and a* however I got 36/50 on my a2 isa not sure what this equals?? Would I still be able to get an a* in the a2 from chem5? Thanks 

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    what reacations do we need to know that are in the catalyisis topic?
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    (Original post by Gazfink)
    We DO need to know them.
    Sodium...yellow flame...white powder
    Magnesium...white flame...white powder
    Alluminum...white flame...white powder
    silicon...white flame...white powder
    Phosphorous...white flame...white powder
    Sulphur...blue flame...choking fumes produced.

    as far as I know this is correct. But please correct me if I'm wrong. Hope that helps.
    We don't need to know the flame tests. There's nothing on the spec to suggest that: Name:  ImageUploadedByStudent Room1370412458.537811.jpg
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    (Original post by SamEastie)
    what he said is in acidic conditions.
    the other ones you need to know are;
    4e- + 2H2O + O2 ---> 4OH-
    4e- + 4H2O ---> 4OH- + 2H2

    (both written as reductions)

    sum of both equations is the same overall as in acidic conditions
    2H2+O2--->2H2O. same cell emf.
    So the one you did is in alkali conditions?
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    (Original post by Affliction)
    We don't need to know the flame tests. There's nothing on the spec to suggest that: Name:  ImageUploadedByStudent Room1370412458.537811.jpg
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Size:  135.9 KB


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    Have you done a past paper recently?
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    (Original post by Dalts)
    Have you done a past paper recently?
    None so far, I was just using the spec to make my point
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    (Original post by Affliction)
    None so far, I was just using the spec to make my point
    Well they do ask about those points that you think aren't in the spec, so I do suggest you start doing the past papers, besides you have less than 2 weeks left :L
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    (Original post by alex7892)
    I got an a overall for as. Howver I am looking to get an a*. In unit 4 I got 108ums which is exactly and a* however I got 36/50 on my a2 isa not sure what this equals?? Would I still be able to get an a* in the a2 from chem5? Thanks 

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    You potentially scraped an A in the ISA.You can still get an A* if you get around 113 UMS out of 120 in Chem5. To achieve this, you'd need approx 84/85 out of 100 in the actual exam.

    This is all assuming you got a low B or higher in your AS modules.
    You got an A at AS. But you'd still need an average of 90 UMS.
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    (Original post by Affliction)
    We don't need to know the flame tests. There's nothing on the spec to suggest that: Name:  ImageUploadedByStudent Room1370412458.537811.jpg
Views: 221
Size:  135.9 KB


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    Point 75: Write equations for the formations of oxides from elements & describe the trends.

    Its very vauge, but the specification is. But can't it be argued that there is a trend in what colour exists when reacting with oxygen. Oxides are usually formed by burning them.
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    (Original post by Dalts)
    Well they do ask about those points that you think aren't in the spec, so I do suggest you start doing the past papers, besides you have less than 2 weeks left :L
    Okay, thanks for the advice but I started my chem4 papers 2 weeks before the exam as well, I don't like doing them too early.


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    (Original post by Gazfink)
    Point 75: Write equations for the formations of oxides from elements & describe the trends.

    Its very vauge, but the specification is. But can't it be argued that there is a trend in what colour exists when reacting with oxygen. Oxides are usually formed by burning them.
    Okay sure, yea I guess there's no harm learning them


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    (Original post by lifeisgood2012)
    So the one you did is in alkali conditions?
    no, mine is just the normal one you need to know
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    (Original post by Affliction)
    We don't need to know the flame tests. There's nothing on the spec to suggest that: Name:  ImageUploadedByStudent Room1370412458.537811.jpg
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Size:  135.9 KB


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    we do need to know them
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    (Original post by SamEastie)
    we do need to know them
    Don't we just need to know the colours period 3 elements burn in oxygen for the periodicty section?
 
 
 
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