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Thread: I don't suppose!

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    I Am A Princess! shelley bda's Avatar
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    Red face I don't suppose!

    There are any scientists around that can help my 14 year old with his science homework please?????

    He's been asked to research "what happens INSIDE an exothermic reaction?" he knows what this exothermic thingy is but has no clue about what happens inside of it. Google throws up nothing and dumbass Mother has no clue either!

    I know you Hexus Peeps are very helpful and knowledgeable!!! thank you xx


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    Senior Member Tumble's Avatar
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    Re: I don't suppose!

    I think it has something to do with the covalent bonds between the molecules breaking down and producing heat as a result... long time since I did chemistry though, so may be a teeny bit inaccurate/plain-assed wrong

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    lazy student nvening's Avatar
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    Re: I don't suppose!

    im guessing it would be that the bonds of the reactants are broken which uses x amount of energy and then new bonds form to produce the product(s) which gives out y amount of energy (heat)

    in an exothermic reaction x is smaller than y and thus heat is released

    EDIT: you might as well get him onto enthalpy profiles while your at it...
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    Re: I don't suppose!

    Thank you both for such quick replies very useful indeed!

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    Does he need a reason? Funkstar's Avatar
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    Re: I don't suppose!

    The chemicals I use for work (epoxy resins) are exothermic. I never thought to ask what goes on during this reaction. So thanks for the thread, this could be interesting.

    Actually, perhaps looking up epoxy resin reactions may give some detail on the subject.

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    jim
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    Re: I don't suppose!

    By nature, making bonds = energy created, breaking bonds = energy used up.

    In an exothermic reaction, energy out > energy in, so therefore bonds made > bonds broken.

    If you want to get more specific, different bonds have different energy values, so the types of bonds are also important. But at a basic level, that's what's going on .

    For example, you might be told that 2 H2 + O2 = 2 H2O. In other words, 4 hydrogen atoms plus 2 oxygen atoms = 2 water molecules.

    But more accurately, it's 2 H2 --> 4H (so two hydrogen-hydrogen bonds are broken to make 4 unattached hydrogen atoms) and O2 --> 2 O (so one oxygen-oxygen bond is broken to make 2 unattached oxygen atoms). And then they reform as 2 H2O, which means four hydrogen-oxygen bonds are made.

    Considering the energies of each individual bond, you can add them all together to work out whether the amount of energy decreases or increases - and thus whether the reaction is endothermic or exothermic.
    Last edited by jim; 02-03-2010 at 09:51 PM.

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    lazy student nvening's Avatar
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    Re: I don't suppose!

    Bond breaking and bond making

    For a chemical reaction to occur bonds must break before new bonds can be made. When bonds break energy is absorbed (endothermic). When bonds form, energy is released (exothermic).

    If the energy absorbed whilst making bonds is greater than the energy transferred to the surroundings as bonds are made, then an endothermic reaction will occur.

    Whereas, if the energy released on bond formation is greater than that absorbed through breaking bonds then an exothermic reaction is observed.
    http://www.s-cool.co.uk/alevel/chemi...y-changes.html

    Good site to bookmark for future homeworks and the dreaded exam time!
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    Re: I don't suppose!

    Yep the above two are pretty much correct.

    In an exothermic reaction the energy required to break the bonds is less then the energy produced from the new bonds forming. Energy is therefore released into the surrounding in the form of light, heat and sound.

    Endothermic is the exact opposite, energy is absorbed from the surroundings.



    And you might as well throw in some semi complicated graphs as well, I used to do it all the time with my hw. It was all good until the teachers made me explain them

    Quote Originally Posted by nvening View Post
    http://www.s-cool.co.uk/alevel/chemi...y-changes.html

    Good site to bookmark for future homeworks and the dreaded exam time!
    I used to use that site for my GCSE which was about 5 years ago now, very useful site

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    Re: I don't suppose!

    Just explain that delta (triangle) H means the 'change in' H

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    Re: I don't suppose!

    Your all amazing! thank you very very much!!! Luke is currently scrabbling away in his science book whilst sat in front of this thread. xXx

    That link is great btw Nvening! Luke has it bookmarked

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    Re: I don't suppose!

    Now throw in some stuff about entropy changes to really impress the teacher.

    Give some Hz to help where it hurts: BOINC Folding@Home

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    Re: I don't suppose!

    Quote Originally Posted by nvening View Post
    im guessing it would be that the bonds of the reactants are broken which uses x amount of energy and then new bonds form to produce the product(s) which gives out y amount of energy (heat)

    in an exothermic reaction x is smaller than y and thus heat is released

    EDIT: you might as well get him onto enthalpy profiles while your at it...
    Yup. Which is why some reactions require an energy input (heat) to get them started.

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    Senior Member oolon's Avatar
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    Re: I don't suppose!

    Wiki link

    A rather nice GCSE one I include this because the previous diagrams don't talk about activation energy, everything would just catch fire if it was not for it.
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    Re: I don't suppose!

    They didn't teach this when I was at school !! If they did I was sick that day.

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    Re: I don't suppose!

    Think i had to do this for my coursework - burning alcohols and measuring the energy released, i miss school
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    Re: I don't suppose!

    Looks like fairly standard GSCE Chem from what I remember, but I find it hard to remember GCSE because I then (more fool me) went and did 3 science A-Levels! I seem to remember having big tables of enthalpy values (i.e. the energy used in breaking, or produced in creating, a particular bond) and drawing enthalpy graphs like the ones shadowmaster provided. You get very similar tables for the electrical potential of various chemicals when you start doing electrolysis, too - a lot of GCSE Chem can be boiled down into tables!

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