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    (Original post by Sharma)
    TiCl4 is correct thats what i got, i done foundation and hfhf, went quite well. There wasnt many calculations in foundation this time around. What did you get for the last question in foundation? the one with why nitrogen was higher than oxygen or sumthin like that
    Was trends in atomic radii

    http://www.chemguide.co.uk/atoms/pro.../atradius.html
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    Btw, for the bromine isomers question you didn't have to draw the isomers that could be formed from that reaction, the question was just 'Draw three structural isomers with the molecular formula C3H6Br2'.
    1,1 / 1,2 / 1,3 / 2,2 are all fine.
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    Are you sure? If so then I am pleased =)

    I thought there was something more complex about it, so I scribbled my first isomers out and did a couple of different ones. 1,2 1,1 2,2

    What did you get for that rocket fuel ammonia thing? I said that the N-N triple bond was highly exothermic on formation so it would propel the rocket. Probably wrong...

    Here
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    From talking to people, I still haven't come any closer to answering that question. Maybe ammonia would have too low an activation energy? Stupid question.
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    I wrote that ammonia's activation energy is too low, so it could ignite too easily.

    Yeah I'm pretty sure that's what the question was Trolley.
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    (Original post by shyopstv)
    From talking to people, I still haven't come any closer to answering that question. Maybe ammonia would have too low an activation energy? Stupid question.
    I put that ammonia had less energy per mole than N2H4 (cause it said 1g of each had about the same energy) so it is less efficient...

    -Kavanne
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    Well my thinking was this right: N2H4 has 2 nitrogens and it makes the N-N triple bond. Bond formation is exothermic and this N-N triple bond was a beast of an exothermic formation. So I thought it might explode almost and provide sufficient energy for a takeoff of a rocket. Ammonia only has 1 N in it, but I was too distracted by my cool idea to think that you could just go 2NH3 + O2 etc...
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    It was a 'suggest' question, so they'll probably give marks for several different ideas.
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    ammonia had less energy per mole than N2H4 (cause it said 1g of each had about the same energy) so it is less efficient...
    Thats good i wrote the same thing!!
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    (Original post by Redeyejedi)
    Thats good i wrote the same thing!!
    Doesn't mean it's right though! :eek:

    -Kavanne
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    i think its to do with the products being gases, at least thats what i could remember from a past paper
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    (Original post by Kavanne)
    I put that ammonia had less energy per mole than N2H4 (cause it said 1g of each had about the same energy) so it is less efficient...

    -Kavanne

    aaaaargh nightmare!!! :eek:

    in my freaked out exam taking state I was making up my own molecule being NH4 and didnt mention anything about n-n triple bond.

    and i messed up the enthalpy of combustion thing (no hess law, the one thing irevised then didnt do)

    im now going to go and have a cry. :mad:
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    The answer to the ammonia question must be something to do with bond enthalpies, as it said to use the table of mean enthalpies in your answer.
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    answer I put for rocket fuel (i think);

    It is because the energy created in making the O-H bonds in water exceeds the energy needed to break the extra NH bond (i.e, more energy is created per amount put in)
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    for the ammonia question i said something like the N-H bond has a lower bond enthalpy than the N-N bond. is that correct? how many marks was that worth anyway?

    for the CFC's question do you think 'it is able to extinguish fires' is a property?
    i also said the use as aerosol propellant cos its easily turned from gas to liquid. is that correct does anyone know?
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    also does any1 remember how many marks the question about why N2H4 rather than NH3 is used was worth? was it 1 or 2?cheers xxx
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    Only 1 mark.

    They said the enthalpy change of combustion (I'm assuming per mole) of NH3 and N2H4 was roughly the same...so it had to be something else.

    Might it be that you need 2 moles of NH3 to make that N-N triple bond? Rather than 1 of N2H4.
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    ah well if it was only one mark then it dnt matter too much i guess? it was probably stating something really obvious but not sure what that something actually is lol
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    did ne1 for chains and rings get 3 sumthing for the mass of the tablet? n what did u say the infra red spec. was showing?
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    (Original post by Trolley)
    Only 1 mark.

    They said the enthalpy change of combustion (I'm assuming per mole) of NH3 and N2H4 was roughly the same...so it had to be something else.

    Might it be that you need 2 moles of NH3 to make that N-N triple bond? Rather than 1 of N2H4.
    They said the enthalphy change for 1g of each was the same, so per mole, they will be different.

    -Kavanne
 
 
 
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