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    (Original post by seph_muriel)
    I have absolutely no idea on how to answer this question:
    Suggest 2 reasons why standard enthalpy changes of combustion determined experimentally are less exothermic than the calculated theoretical values. (for 2 marks OCR Chemistry A)
    Incomplete combustion so not everything has burned completely. And heat lost to surroundings

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    guys if your doing aqa try the a level papers not just AS because in the new spec papers there is stuff for paper 2 we can use especially in A Level Paper 3
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    (Original post by mali473)
    Incomplete combustion so not everything has burned completely. And heat lost to surroundings

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    Why is it incomplete combustion?
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    How do you work this out please?
    Compound F contains C, H and O only. O contains 54.2% oxygen by mass. Mr of F = 118 gmol-1
    Show that the molecular formula of F= C4H6O4 [2 MARKS]
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    (Original post by seph_muriel)
    Why is it incomplete combustion?
    Not enough Co2 is available or other conditions not favourable for the reactants to combust
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    (Original post by Hellper)
    Not enough Co2 is available or other conditions not favourable for the reactants to combust
    Not enough Oxygen is available for the reactant to burn in

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    (Original post by Hellper)
    Not enough Co2 is available or other conditions not favourable for the reactants to combust
    Not enough oxgen is available to burn the reactant in therefore carbon monoxide, soot and water are produced as a result of this.

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    (Original post by mali473)
    Incomplete combustion so not everything has burned completely. And heat lost to surroundings

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    I thought that that is to do with covalent character??
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    (Original post by mali473)
    Not enough oxgen is available to burn the reactant in therefore carbon monoxide, soot and water are produced as a result of this.

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    (Original post by bat_man)
    I thought that that is to do with covalent character??
    yeah me too?
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    (Original post by hafsa473)
    yeah me too?
    yeah look at this.

    Differences between theoretical and Born Haber (experimental)lattice enthalpies

    The Born Haber lattice enthalpy is the real experimental value.When a compound shows covalent character, the theoretical and theborn Haber lattice enthalpies differ. The more the covalent characterthe bigger the difference between the values.

    When the negative ion becomes distorted and more covalent we say it becomes polarised. Themetal cation that causes the polarisation is called more polarising if it polarises the negative ion.

    Ionic with covalent character - The charge cloud is distorted .The theoretical and the experimental Born Haber lattice enthalpies will differ

    100 % ionic - the ions are spherical.The theoretical and the born Haber latticeenthalpies will be the same
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    For the equation is the question asking for the discharging or charging equation?

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    (Original post by Glavien)
    For the equation is the question asking for the discharging or charging equation?

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    charging, just reverse everything
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    (Original post by K3001N)
    charging, just reverse everything
    Why would you say charging? I thought it would be discharging as the question states it's 'recharged' already.


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    Unit 5 is going horrible idk why I just find it so hard


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    (Original post by Supermanxxxxxx)
    Unit 5 is going horrible idk why I just find it so hard


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    Are you doing AQA??
    There is a lot of content no doubt divide your topics and cover one part of the spec each day like eg from transition metals do catalysis one day then ox States the other
    When you finish the content and go over it I'm sure you'll find it okay!
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    (Original post by Supermanxxxxxx)
    Unit 5 is going horrible idk why I just find it so hard


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    I found unit 5 (aqa) really hard at first too, but if you go over the content enough times, it's all just memory work
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    I'm doing edexcel but still pretty similar and yeah I'll just memorise all the content and then hopefully the papers will be a lot easier


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    http://www.thestudentroom.co.uk/show...7#post65258087

    You people might find posts 5 and 6 useful...
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    Name:  Screenshot_2016-06-01-10-43-31.png
Views: 73
Size:  110.4 KBCan someone explain to me why glycerin has 4 peaks and acetol has 3?
    Why does acetol have a 3:2:1 ratio?
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    What did the nitrogen say when it got baptised?
    ......

    AMINE

    hmm yeah i'll find my way out
 
 
 
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