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    (Original post by jamesl1)
    hey in thermodynamics ive read that smaller ions lead to bigger lattice formation enthalpies due to the charges being closer together etc, but ive also read that with bigger anions you get larger enthalpies due to being distorted by the cation and hence there is slight convalence.

    does anyone know which is correct ?
    I was talking about this earlier in the thread, this is unit 1 stuff i think your reffering to, its knowledge about how smaller positive ions are more polarising (e.g. Li+ is more polarising than Na+)
    And larger anions are more easily polarised so when combined with a small positve ion, you would have more covalent character than you would ionic (in the lattice),
    and a combination of both ionic and covalent means you need more energy to break your lattice


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    (Original post by teddyWS)
    Also what leads to strong ionic bonding?
    small ions?
    You get ionic bonding when you have a large difference in electronegativity between the two ions
    and the electrons are completely transferred not shared, so NaCl is more ionic than LiCl because Li+ is more polarising than Na+ so it would distort the electron cloud around the negative ion (the Cl-)



    Oh and the more charged the Negative ion has, the more likely you will have some covalent character, again because theyre easily polarised like Na2O (O2-)
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    (Original post by teddyWS)
    Also what leads to strong ionic bonding?
    small ions?
    not always, but greater charge density does

    the ion can be small but have a low charge, another ion may be big but might have very high charge,

    for example, if you look at CL-, it is a smaller ion than Br- but has the same charge, therefore higher charge density on CL- so stronger ionic bonding
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    thank you
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    (Original post by Arab_Empress)
    You get ionic bonding when you have a large difference in electronegativity between the two ions
    and the electrons are completely transferred not shared, so NaCl is more ionic than LiCl because Li+ is more polarising than Na+ so it would distort the electron cloud around the negative ion (the Cl-)



    Oh and the more charged the Negative ion has, the more likely you will have some covalent character, again because theyre easily polarised like Na2O (O2-)
    (Original post by xX.Sabeel.Xx)
    not always, but greater charge density does

    the ion can be small but have a low charge, another ion may be big but might have very high charge,

    for example, if you look at CL-, it is a smaller ion than Br- but has the same charge, therefore higher charge density on CL- so stronger ionic bonding
    thanks! so if polarising does occur does that mean the lattice is weaker than a perfect ionic lattice? what effect would polarisation have on lattice enthalpy? :confused: thanks again
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    will someone pleeeeeeeeeease just go through Q= mc/\T?! I dont have the same textbook as last year, and its crap
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    (Original post by ceeebs)
    will someone pleeeeeeeeeease just go through Q= mc/\T?! I dont have the same textbook as last year, and its crap
    Q= enthaply change
    m= mass (usually use a liquid so mass=volume unless they tell you otherwise!)
    c= heat capacity (a fixed value that they usually state)
    deltaT = change in tempereature

    but isnt this unit 2?
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    (Original post by BethBeth)
    Adsorption only happens on heterogeneous catalysts, where reactants are adsorbed usually by a metal catalyst, react and then are released...

    Homogeneous catalysts are in the same phase as reactants (usually aqueous) so surely they can't be adsorbed?

    (Correct me if I'm wrong people).
    ahh, my mistake, thankyou!
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    (Original post by teddyWS)
    thanks! so if polarising does occur does that mean the lattice is weaker than a perfect ionic lattice? what effect would polarisation have on lattice enthalpy? :confused: thanks again
    Perfect ionic lattice means all ionic bonds are perfectly polarised (i think), If the value for the lattice enthalpy worked out through an experiment is higher than the theoretical value then that means the forces between ions are stronger than ionic bonds.... so must be covalent characteristics between ions because covalent bonds are stronger than ionic bonds
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    (Original post by addvic)
    Q= enthaply change
    m= mass (usually use a liquid so mass=volume unless they tell you otherwise!)
    c= heat capacity (a fixed value that they usually state)
    deltaT = change in tempereature

    but isnt this unit 2?
    yep synoptic, i think Q= heat energy or something because i'm pretty sure deltaH=enthalpy change

    so you use DeltaH=Q/n
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    (Original post by al_habib)
    you guys have you done ALL the past papers i mean from 2002-2011
    Yep I finished them last week, having to just do the recent ones again so that I can refresh my mind :P
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    (Original post by teddyWS)
    thanks! so if polarising does occur does that mean the lattice is weaker than a perfect ionic lattice? what effect would polarisation have on lattice enthalpy? :confused: thanks again
    When you get polarisation, you have covalent character
    im sure ure aware that covalent bonds and ionic bonds are strong
    when you both positve iones and negative ions together forming a lattice you get ionic bonds, that additional polarisation means you now have covalent bonds additional to the ionic bonds

    ionic + covalent = greater lattice enthalpy
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    hey could anyone help me with redox equations im just not sure when you include only one reagent and product for example in the specimen paper,

    3 (a)An aqueous solution of sulfur dioxide was reacted in separate experiments as follows.

    Reaction 1 with HgO
    H2O + SO2 + HgO ? H2SO4 + Hg

    Reaction 2 with chlorine
    2H2O + SO2 + Cl2 ? H2SO4 + 2HCl

    (ii) Show, by writing a half-equation, that this oxidising agent in reaction 1 is an
    electron acceptor.
    ................................ ................................ ................................ ................................ ..
    (iii) Write a half-equation for the oxidation process occurring in reaction 2.
    ................................ ................................ ................................ ................................ ..
    (iv) Write a half-equation for the reduction process occurring in reaction 2.
    ................................ ................................ ................................ ................................ ..

    the answer for ii is Hg 2+ + 2e- -------> Hg

    the answer for iii is 2H2O + SO2 ? H2SO4 + 2e-

    why dosnt the oxygen on the Hg come into the half equation?

    Thanks
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    21. H2(g) + 2OH-(aq) ? H2O(l) + 2e-

    22. O2(g) + 2H2O(l) + 4e- ? 4OH-(aq)


    what are these equations for the hydrogen-oxygen fuel cell
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    Jan 10, q8c anyone???
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    Does anybody have the Jan11 QP they can upload? Thanks
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    (Original post by Arab_Empress)
    When you get polarisation, you have covalent character
    im sure ure aware that covalent bonds and ionic bonds are strong
    when you both positve iones and negative ions together forming a lattice you get ionic bonds, that additional polarisation means you now have covalent bonds additional to the ionic bonds

    ionic + covalent = greater lattice enthalpy
    does greater lattice enthalpy mean the bonds are stronger or weaker ?
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    Whats the reaction of (Al(h20)6) with excess OH-?
    I thought it was (Al(h20)6) +4oH- === (Al(OH)4)- +6H20, but I just did june 2010 paper and it said [Al(OH)6]3- was formed
    Which is correct?!
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    (Original post by cheeseisnice)
    Whats the reaction of (Al(h20)6) with excess OH-?
    I thought it was (Al(h20)6) +4oH- === (Al(OH)4)- +6H20, but I just did june 2010 paper and it said [Al(OH)6]3- was formed
    Which is correct?!

    [Al(OH)6]- and [Al(OH)6]3- are both correct.
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    hey could anyone help me with redox equations im just not sure when you include only one reagent and product for example in the specimen paper,

    3 (a)An aqueous solution of sulfur dioxide was reacted in separate experiments as follows.

    Reaction 1 with HgO
    H2O + SO2 + HgO ? H2SO4 + Hg

    Reaction 2 with chlorine
    2H2O + SO2 + Cl2 ? H2SO4 + 2HCl

    (ii) Show, by writing a half-equation, that this oxidising agent in reaction 1 is an
    electron acceptor.
    ................................ ................................ ................................ ................................ ..
    (iii) Write a half-equation for the oxidation process occurring in reaction 2.
    ................................ ................................ ................................ ................................ ..
    (iv) Write a half-equation for the reduction process occurring in reaction 2.
    ................................ ................................ ................................ ................................ ..

    the answer for ii is Hg 2+ + 2e- -------> Hg

    the answer for iii is 2H2O + SO2 ? H2SO4 + 2e-

    why dosnt the oxygen on the Hg come into the half equation?

    Thanks
 
 
 
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