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    Thanks Ramaya

    Another question, for Salters Chem, do we need to be able to compare octane numbers? For example: 'Arenes have a high octane number with relation to cycloalkanes'
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    (Original post by LS.)
    Thanks Ramaya

    Another question, for Salters Chem, do we need to be able to compare octane numbers? For example: 'Arenes have a high octane number with relation to cycloalkanes'
    I don't remember ever being taught that you need to compare them, but i think it's useful to state which one has a higher/lower rating (if that makes any sense). I havn't done this since January so i've forgotten a fair amount.
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    (Original post by Ramaya)
    I don't remember ever being taught that you need to compare them, but i think it's useful to state which one has a higher/lower rating (if that makes any sense). I havn't done this since January so i've forgotten a fair amount.
    Don't worry it makes sense. I've come across it in my revision guide (salters specific) and I can't remember being taught it (but that wouldnt surprise me) or seeing it in the CS or CI.
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    (Original post by LS.)
    When writing the formula for combustion, which of these is more acceptable? It says in my revision guide either, but I thought when writing about combustion, you only used one mole....

    Either: C(2)H(6) + 3.5 O(2) --> 2CO(2) + 3H(2)0

    Or: 2C(2)H(6) + 7 O(2) --> 4CO(2) + 6H(2)0
    it depends on the question
    if it's asking about standard enthalpy change for ethane combustion you should use the first as it is one mole that is combusted.

    but if it just says construct an equation to show complete combustion then either should be acceptable. but i'd use the first for both circumstances.
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    (Original post by PaX)
    Hi,

    Can anyone explain what is meant by

    "dynamic"

    and

    "Equilibrium"
    Dynamic equilibrium definition you will most likely be a 2 mark question.
    i think it's just:
    -forward rate of reaction is equal to the reverse rate of reaction
    -in a closed system

    or something like that
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    (Original post by hihihihi)
    Dynamic equilibrium definition you will most likely be a 2 mark question.
    i think it's just:
    -forward rate of reaction is equal to the reverse rate of reaction
    -in a closed system

    or something like that
    Yeah "in a closed system" or "no macroscopic changes are observable".
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    (Original post by mik1a)
    For Edexcel you need to know the following reactions by heart from organics, for all those who say it's easy:

    Alkanes: Complete and incomplete combustion

    How do we find the equations of incomplete combustion????
    plz help!
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    (Original post by KOH)
    How do we find the equations of incomplete combustion????
    plz help!
    for incomplete combustion of alkanes, carbon monoxide (CO) and water (H2O) are formed, rather than CO2+H2O
    then balance like normal.
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    (Original post by the_wizzz)
    I find Module 3 hard. Does anyone know any good sites that have a list of all the experiments, etc you need to know. BTW, I'm doing Edexcel.
    this is my unit 3 notes - some gaps but it's mostly good
    Attached Files
  1. File Type: doc some tests.doc (26.0 KB, 199 views)
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    Dynamic equilibrium:

    - Forward and backward reactions occur at equal rate
    - Meaning constant constant concentration of products and reactants
    - In a closed system

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    (Original post by Pegasus)
    Oooh!

    I'm doing Edexcel Nuffield and I'm having quite a bit of dificulty understanding the entire concept of electrophilic, nucleophilic substitution, addition etc (topic 10 stuff about halogenoalkanes and also so some topic 8 stuff on alkenes) does anyone know any good websites which goes through the topic nice and slowly and clearly, because I find the student's book completly incomprehensable?

    Greatly appreciated

    im doin nuffield as well and the book is completely useless. does anyone have the markschemes for the end of chapter exam questions? also any good revision sites wud be helpful.

    can anyone help me out with working out enthalpy change of combustion?
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    For Salters, do we need to know the equation:

    Energy Density = Enthalpy of combustion x Amount of fuel in 1kg

    ETA:

    Do we also need to know the stages in the extraction of bromine and copper?
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    im not sure about the pressure used for the contact process of sulphuric acid... is it 200 atm? thats wt my teacher said...
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    (Original post by z!D4N)
    im not sure about the pressure used for the contact process of sulphuric acid... is it 200 atm? thats wt my teacher said...
    it's 2, i'm sure ur teacher said 2 as well
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    (Original post by z!D4N)
    im not sure about the pressure used for the contact process of sulphuric acid... is it 200 atm? thats wt my teacher said...
    No, 2 atm since this gives a reasonable yield and pushes the gases through the plant. Any higher would not justify the cost.
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    (Original post by Whywhywhy)
    No, 2 atm since this gives a reasonable yield and pushes the gases through the plant. Any higher would not justify the cost.
    thx

    man... i want some challenge in chemistry... it seems like i know everything... anybody have any challenging questions which they think are hard?
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    (Original post by z!D4N)
    thx

    man... i want some challenge in chemistry... it seems like i know everything... anybody have any challenging questions which they think are hard?
    From the AQA specimen paper
    8. Write an essay on the chemistry of ammonia.

    In your answer you should include a discussion of the bonding in, and the structure of the molecule, considering its industrial preperation and you should bring togeather its reactions in both inorganic and organic chemistry.

    (15)
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    anyone know any good revision sites for edexcel topic 2 chemistry? got my retake a week today!
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    (Original post by Speciez99)
    From the AQA specimen paper
    8. Write an essay on the chemistry of ammonia.

    In your answer you should include a discussion of the bonding in, and the structure of the molecule, considering its industrial preperation and you should bring togeather its reactions in both inorganic and organic chemistry.

    (15)
    shape of ammonia=trigonal pyramidal
    bond angle=107

    bonding=covalent
    ammonia= alkali, turns red damp litmus paper blue

    N2+3H2->2NH3

    conditions=200atm, 450 C
    catalyst=iron

    during the production, the reactants are fed into the chamber and they react. unreacted molecules are fed back into the chamber.

    the ammonia is cooled and liquidified at the end.

    this is all i can remember... btw im not doing AQA.
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    (Original post by LS.)
    Do we also need to know the stages in the extraction of bromine and copper?
    Yep we need to know this, i would be suprised if it wasn't on the exam.
 
 
 
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