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Edexcel IGCSE Chemistry 17th May 2018 (Exam Discussion) watch

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    Hi guys,

    Anyone doing this paper (Either 1C or 1CR) tomorrow?

    I'll be doing 1CR. If you need any help, please feel free to ask
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    please explain to me the topic on addition and condensatiion polymers
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    (Original post by ANAAA222)
    please explain to me the topic on addition and condensatiion polymers
    Sure! First of all, I'm glad to let you know that only addition polymers will appear on the test tomorrow. Condensation polymers are bold in the syllabus, meaning that they will come up on paper 2.

    Addition polymer:

    Basically, these are formed by joining monomers together. For example, the monomer ethene (C2H4), will be joined up together to form the polymer polyethene. As you know from previous units, ethene is unsaturated (has a double bond). The C=C double bond will break to join the monomers together. It will then look like this, which is the repeating unit.


    Name:  Polyethene.png
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    'n' basically represents a lot of monomers joined together. Make sure the single bonds extend out of the brackets on the side, as they link together.
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    (Original post by Harry Xu)
    Hi guys,

    Anyone doing this paper (Either 1C or 1CR) tomorrow?

    I'll be doing 1CR. If you need any help, please feel free to ask
    (Original post by Harry Xu)
    Hi guys,

    Anyone doing this paper (Either 1C or 1CR) tomorrow?

    I'll be doing 1CR. If you need any help, please feel free to ask
    yup, 1cr, along with another exam and the first day of ramadan!
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    I cannot do chemistry at all! Please explain about equilibrium!
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    (Original post by ANAAA222)
    please explain to me the topic on addition and condensatiion polymers
    Condensation polymers are slightly more tricky. I won't go into too much depth, and I'll cover just enough for edexcel IGCSE.

    You need to know that nylon is a condensation polymer, and this process creates water as well as the polymer.

    I'll explain more if you need but as long as you memorise the above you should be fine.
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    (Original post by mfar)
    yup, 1cr, along with another exam and the first day of ramadan!
    Good luck!
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    (Original post by ellie145)
    I cannot do chemistry at all! Please explain about equilibrium!
    Ok equilibrium isn't as hard as you think. It's just common that this can be an application question, so you may need to think about it.

    It is section 4d of the syllabus.

    If a question about equilibrium comes up, it'll probably ask you to explain the dynamic equilibrium. These are the 3 points you need to answer (on the mark scheme ALWAYS)
    - Forward and backward reaction occur at same rate
    - Forward and backward reaction occur at same time
    - The mass of reactants and products stays constant

    And onto the slightly more tricky part - predicting the effects of pressure and temperature in reversible reactions.

    First of all, you need to identify whether the forward reaction is exothermic or endothermic. This is often given in the question. If the molar enthalpy is negative, the reaction is exothermic. If the molar enthalpy is positive, the reaction is endothermic.

    OK, so let's use the Haber process of
    Nitrogen + Hydrogen <---> Ammonia

    (That isn't the symbol for reversible but I'm using a computer typing so...)

    The forwards reaction is exothermic. You probably learnt that a high temperature increases yield of the endothermic reaction. The opposite being a low temperature increases yield of exothermic reaction.

    Therefore, in the Haber process, a low temperature should be used. HOWEVER, this is not the case (450 degrees celsius), because rate of reaction will be too slow if the temperature was like 5 degrees. But theoretically, that would create a much higher yield.

    If you have any more queries, feel free to let me know

    I can go through a past paper question if you need me to (if you give the Q of course)
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    Ahh thank you so much, this has really helped me to understand it, you’re going to do so well
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    (Original post by ellie145)
    Ahh thank you so much, this has really helped me to understand it, you’re going to do so well
    Haha I hope Questions like this can be tricky as it links different topics together... Our chem teacher was like, "if you use a really low temperature in the Haber process, you'll have to wait for the products all day (due to little kinetic energy, fewer collisions, and slower rate of reaction)"

    Good luck!
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    Yeah! Thank you, you too
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    (Original post by Harry Xu)
    Ok equilibrium isn't as hard as you think. It's just common that this can be an application question, so you may need to think about it.

    It is section 4d of the syllabus.

    If a question about equilibrium comes up, it'll probably ask you to explain the dynamic equilibrium. These are the 3 points you need to answer (on the mark scheme ALWAYS)
    - Forward and backward reaction occur at same rate
    - Forward and backward reaction occur at same time
    - The mass of reactants and products stays constant

    And onto the slightly more tricky part - predicting the effects of pressure and temperature in reversible reactions.

    First of all, you need to identify whether the forward reaction is exothermic or endothermic. This is often given in the question. If the molar enthalpy is negative, the reaction is exothermic. If the molar enthalpy is positive, the reaction is endothermic.

    OK, so let's use the Haber process of
    Nitrogen + Hydrogen <---> Ammonia

    (That isn't the symbol for reversible but I'm using a computer typing so...)

    The forwards reaction is exothermic. You probably learnt that a high temperature increases yield of the endothermic reaction. The opposite being a low temperature increases yield of exothermic reaction.

    Therefore, in the Haber process, a low temperature should be used. HOWEVER, this is not the case (450 degrees celsius), because rate of reaction will be too slow if the temperature was like 5 degrees. But theoretically, that would create a much higher yield.

    If you have any more queries, feel free to let me know

    I can go through a past paper question if you need me to (if you give the Q of course)
    Hey im sorry but i don't understand the part where you said
    - Forward and backward reaction occur at same rate
    - Forward and backward reaction occur at same time
    - The mass of reactants and products stays constant
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    and also the concentration remains constant
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    And for all the paper 2 folks i predict condensation polymerization will come as its the last paper of our syllabus, they will put all the stuff that they haven't included previously (did all the past papers and no question about it came up)
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    (Original post by ItsMisho)
    Hey im sorry but i don't understand the part where you said
    - Forward and backward reaction occur at same rate
    - Forward and backward reaction occur at same time
    - The mass of reactants and products stays constant
    Hey, this is basically dynamic equilibrium e.g.

    white anhydrous copper sulfate + water <-----> blue hydrated copper sulfate

    If you get a bottle of hydrated copper sulfate, it looks blue and doesn't look like anything has happened. BUT ACTUALLY, this reversible reaction is constantly happening. That's why the equilibrium is at a dynamic state (dynamic literally means constant state).

    So the reaction inside the bottle is happening, yet we cannot see it because the reactants and products, they are constant, since the same amount of products are produced, and the same amount of reactants are produced.

    Understood?
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    (Original post by studybydiffusion)
    And for all the paper 2 folks i predict condensation polymerization will come as its the last paper of our syllabus, they will put all the stuff that they haven't included previously (did all the past papers and no question about it came up)
    Wait what we're the last batch?
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    (Original post by Harry Xu)
    Wait what we're the last batch?
    Yep they've slightly altered the syllabus for the 9-1 batch, but we're the last A* batch.
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    Any ideas of what the big-markers will cover, at all?
    In either exam
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    (Original post by jmsk_)
    Any ideas of what the big-markers will cover, at all?
    In either exam
    I'd love a 10 mark question on condensation polymerisation of explaining how dicarboxylic acid reacts with diamine to form nylon and water but that won't come up because it's not on the syllabus...

    There aren't even big markers in chem compared to bio. I'd say maybe comparing the choices of fermentation / industrial production of ethanol?

    Maybe also some electron transfer question or bonding question for 5 marks e.g. why does sodium have lower melting and boiling point than sodium chloride.
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    I am also doing the chem paper pls explain me an easy way to do moles
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