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    (Original post by fellowgrip)
    Yeh, it is, cheers for help though
    Anytime!


    FAO: Everyone

    When a question asks you to write the rate equation for this reaction: I wrote
    Rate =

    according to the mark scheme it's K= Rate over reactants?
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    (Original post by haydyb123)
    Anytime!


    FAO: Everyone

    When a question asks you to write the rate equation for this reaction: I wrote
    Rate =

    according to the mark scheme it's K= Rate over reactants?
    Looking at wrong part of the mark scheme, silly me
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    (Original post by haydyb123)
    Looking at wrong part of the mark scheme, silly me
    Suggest why the lattice enthalpy of an ionic solid cannot be measured directly?!

    Ms:
    Impossible/difficult to get gaseous ions (without them reacting)/difficult to vapourise ions and measure the enthalpy change at the same time/


    Textbook: Its impossible to form one mole of ionic lattice from gaseous ions

    2 different things and not sure I know what they are talking about!

    Shed some light :rolleyes:
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    (Original post by arvin_infinity)
    Suggest why the lattice enthalpy of an ionic solid cannot be measured directly?!

    Ms:
    Impossible/difficult to get gaseous ions (without them reacting)/difficult to vapourise ions and measure the enthalpy change at the same time/


    Textbook: Its impossible to form one mole of ionic lattice from gaseous ions

    2 different things and not sure I know what they are talking about!

    Shed some light :rolleyes:
    Not trying to patronise you by writing out the definition of Lattice Enthalpy but it i'm trying to show you how to see it like I do...

    Say for instance NaCl(s)

    Na+ (g) + Cl-(s) -> NaCl(s)

    Trying to get the exact volumes of these two gaseous ions to form one mole of NaCl is near enough impossible to do, add to the fact that Na+ and Cl- will be extremely reactive with anything else, and it makes it virtually impossible to directly measure lattice enthalpy.

    Does that sort of help?
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    (Original post by haydyb123)
    No I think it's all legacy!
    Thanks...do you know if MgCO3 is a gaint ionic lattice?
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    (Original post by M_I)
    Thanks...do you know if MgCO3 is a gaint ionic lattice?
    I think I have seen it referred to as one!
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    (Original post by haydyb123)
    Not trying to patronise you by writing out the definition of Lattice Enthalpy but it i'm trying to show you how to see it like I do...

    Say for instance NaCl(s)

    Na+ (g) + Cl-(s) -> NaCl(s)

    Trying to get the exact volumes of these two gaseous ions to form one mole of NaCl is near enough impossible to do, add to the fact that Na+ and Cl- will be extremely reactive with anything else, and it makes it virtually impossible to directly measure lattice enthalpy.

    Does that sort of help?
    Stop patronising meee!:P am the GOD of chemistry
    Perhaps u meant cl(g)+..
    So ur saying gaseous ions are too reactive and might react with something else when we measuring enthalpy change
    Makes more sense now :rolleyes:
    But if you had looked at the other answer is totally different to this. That one is talking

    about vaporising ions which is more of a problem in measuring atomisation enthalpy
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    (Original post by arvin_infinity)
    Stop patronising meee!:P am the GOD of chemistry
    Perhaps u meant cl(g)+..
    So ur saying gaseous ions are too reactive and might react with something else when we measuring enthalpy change
    Makes more sense now :rolleyes:
    But if you had looked at the other answer is totally different to this. That one is talking

    about vaporising ions which is more of a problem in measuring atomisation enthalpy
    Haha!
    Hmm, not to try and shun your questions, but I'm not sure if the spec contains; specifics of why you can't measure all of the enthalpies directly. Therefore I think it will be unlikely that it will be examined... Thank the real gods of Chemistry
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    (Original post by Limesasquatch)
    TBH, this unit is a piece of p*ss. Yet i have been unable to score well in any past paper!!
    It is very easy, the thing is you don't have to do a lot to go wrong. what kind of marks are you getting?
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    why is the h-o-h bond angle in the water ligand 107 rather than 104.5?
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    in [cu(h20)6]2+
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    F325 you can just.... :hand:

    Im going back to F324 revision, plan on squeezing out marks from that :ahee:
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    also what do we need to know on neutralisation curves?
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    (Original post by entertheOJI)
    It is very easy, the thing is you don't have to do a lot to go wrong. what kind of marks are you getting?
    63/100 in the first one, and 54/100 in the second one!
    I'm supposed to be getting an A* lolz
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    (Original post by wilsea05)
    FeO4 2- + H+ -------> O2 + H20 + Fe 3+
    Fe6+ Fe3+ - reduced by 3, so you want an even number really as O2- -> O and you can't have 1.5O2- lol
    so if you try
    2Fe6+ -> 2Fe3+ overall reduction of 6
    you have 8 O2- ions now, but you only want 3 of them to be oxidized to O2
    so that means you'll have 1.5 O2, and 5H2O
    you don't really want halves though, so double it again to...
    4Fe6+ ->4Fe3+ overall reduction of 12
    16O2-, so you want 6 O2- to be reduced, giving you 3O2 molecules
    this leaves you with 10 O2-, which stay as O2-
    10 O2- means you must have 10H2O, so to balance that you need 20H+

    giving overall equation 4FeO42- + 20H+ -> 4Fe3+ + 10 H2O + 3O2

    probably would've taken me a LOT longer if you didn't post the answer haha
    Hey, Thanks for this tbh i dont understand the first step..Why did you put 2 in front of the fe04? you could have put 2 in front of the fe3+, to balance the charges on the fe?
    OMG I'm so dumb
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    (Original post by KateSW)
    Okay, I didn't actually try to do it before, and you're right it's really hard!
    Obviously I can see that the answer is balanced, but i have no idea how you'd go about doing that! If your teacher can't do it, i've got no chance i'm afraid! Sorry I wasn't more help.
    ohh no worries, thanks anyway
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    (Original post by volvicstar)
    why is the h-o-h bond angle in the water ligand 107 rather than 104.5?
    In water, there is 2 bondings pairs and 2 lone pairs (on the oxygen) this increases repulsion between electrons,
    Whereas in the ligand there, is 3 bonding pairs and 1 lone pair, which minimizes the repulsion between electrons, hence why bond angle is 2.5 degrees more!
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    In the specimen paper Q 4B)

    They have started a born-haber cycle, they have done the enthalpy change of atomisation of Ca
    Ca(s)+0.5O2(g) -------> Ca(g)+0.5O2(g)

    Then after this step they have done the enthalpy change of atomisation of O2 but when they have done this step they show Ca as in the solid state again on the line above. Is this meant to be in the gaseous state or is my next step meant to be the enthaply of atomisation of Ca again?
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    (Original post by haydyb123)
    In water, there is 2 bondings pairs and 2 lone pairs (on the oxygen) this increases repulsion between electrons,
    Whereas in the ligand there, is 3 bonding pairs and 1 lone pair, which minimizes the repulsion between electrons, hence why bond angle is 2.5 degrees more!
    Hey i was wondering if you could explain something to me please?

    If you've done the june 2010 paper, question 3d (the one on acid base pairs)

    The equation is: HNO3 + CH3CH2COOH -----> ---- ------

    I wrote: HNO3 + CH3CH2COOH ----> CH3CH2COO- + H2NO3

    This was wrong and it was CH3CH2COOH2 + HNO3-

    How do i know this? They both acids so how do i know which proton is going where?

    Would you be able to explain how you would tackle question 7d in that same paper? I did it all the way till finding the concentration of undiluted hydrogen peroxide? I could do the oxygen part. Just that undiluted part please

    Thank you, really appreciate this
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    Hi all, i'm finding the past exam questions too easy, does anyone here have a list of stretch and challenge questions that i'll struggle to do? thanks.
 
 
 
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