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    Chem help..... :O

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    The Banker
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    Re: Chem help..... :O

    Post by The Banker on Sat Dec 19, 2009 6:45 pm

    da rest of da Q...
    b) what is the enthalpy change obtained in (a) called?
    >> enthalpy of formation..
    c)Draw an enthalpy level diagram to represent the enthalpy change for the combstion of graphite. Show both the enthalpy levels of the reactants and products and an energy profile (what da hell is that?!?!??) which represents the activation energy of the reaction?

    >> again i'm totally baffed
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    Re: Chem help..... :O

    Post by The Banker on Sat Dec 19, 2009 6:45 pm

    Ahmed IV wrote:Those values are the enthalpies of formation, correct?
    yes...
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    Steve
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    Re: Chem help..... :O

    Post by Steve on Sat Dec 19, 2009 6:47 pm

    For C draw a snail wearing a top hat. That always gets you top marks Smile
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    Re: Chem help..... :O

    Post by Ahmed on Sat Dec 19, 2009 6:48 pm

    Then they should be 0(zero) Marwa. Where did you get those numbers from???

    This however does have an enthalpy of formation: CH3COOH


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    Re: Chem help..... :O

    Post by The Banker on Sat Dec 19, 2009 6:50 pm

    its in da question...
    AHHHH!!
    i'm really gonna fail that test in jan Sad
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    Re: Chem help..... :O

    Post by Steve on Sat Dec 19, 2009 6:53 pm

    snail.
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    Re: Chem help..... :O

    Post by Ahmed on Sat Dec 19, 2009 6:54 pm

    Calm down lol.

    Look according to my chem book:

    H2(g) has a Delta H of Formation of 0kJ/mol
    H(g) however, has a Delta H of Formation of 217.94kH/mol

    Are you sure its H2(g)??


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    Re: Chem help..... :O

    Post by The Banker on Sat Dec 19, 2009 6:59 pm

    yes it says H2... but it says that they r enthalpies of combustion..
    damn i'm confusing myself.. :S
    @ Steve: get out of my thread... don't u have media to do or something?
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    Re: Chem help..... :O

    Post by Ahmed on Sat Dec 19, 2009 7:02 pm

    Ok then subtract the sum of the enthalpies of the reactants from the sum of the enthalpies of the products.

    I'm not 100% sure though...


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    Re: Chem help..... :O

    Post by Steve on Sat Dec 19, 2009 7:04 pm

    lol marwa, actully im a master of chemestry and im just trying to help you understand it Sad

    back to studying the media for me Razz
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    Re: Chem help..... :O

    Post by The Banker on Sat Dec 19, 2009 9:22 pm

    Ahmed IV wrote:Ok then subtract the sum of the enthalpies of the reactants from the sum of the enthalpies of the products.

    I'm not 100% sure though...
    thanx anywayz man Smile

    @steve:: since when did chemistry involve snails?
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    Re: Chem help..... :O

    Post by Steve on Sat Dec 19, 2009 9:27 pm

    it doesn't bu the thingy you want to draw looks exactly like a snail in a top hat Smile
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    Re: Chem help..... :O

    Post by The Banker on Sat Dec 19, 2009 9:29 pm

    looooooooooolz
    i guess it does man!!
    i'll remember this 4 da exam Wink
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    Re: Chem help..... :O

    Post by Steve on Sat Dec 19, 2009 9:32 pm

    oh and dont forget an octopus can use 8 walking sticks at once.
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    Re: Chem help..... :O

    Post by The Banker on Sun Dec 20, 2009 3:48 pm

    The thermodynamic equations for the reactions of dilute hydrochloric acid with sodium hydrogencarbonate
    and with sodium carbonate are:
    (i) NaHCO3(s) + HCl(aq) ==>NaCl(aq) + H2O(l) + CO2(g)
    *delta*H = -y kJ mol^-1
    (ii) Na2CO3(s) + 2HCl(aq) ==>2NaCl(aq) + H2O(l) + CO2(g)
    *delta*H = -z kJ mol^-1
    What is the enthalpy change (kJ mol^-1) for the reaction 2NaHCO3(s) ==>Na2CO3(s) + H2O(l) +
    CO2(g)?
    A z - y
    B y - z
    C 2y - z
    D z - 2y
    >> i'm baffed.. :S apparentally da answer is D... but how?
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    Re: Chem help..... :O

    Post by Ahmed on Sun Dec 20, 2009 3:49 pm

    Use Hess's law Smile


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    Re: Chem help..... :O

    Post by The Banker on Sun Dec 20, 2009 3:54 pm

    ohhhhhhhh.
    kk then thanx Smile
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    Re: Chem help..... :O

    Post by Ahmed on Sun Dec 20, 2009 3:56 pm

    NP Wink


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    Re: Chem help..... :O

    Post by The Banker on Wed Dec 30, 2009 5:26 pm

    Effluent water from a factory contains 5.4 ppm Al3+ ions. The mass of Al3+ ions in 1.0dm^3 of water is..

    a) 5.4 mg
    b) 0.146 mg
    c) 0.2 mg
    d)2x10^-4 g


    How do i even start doing this Q :S
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    Re: Chem help..... :O

    Post by Ahmed on Wed Dec 30, 2009 5:30 pm

    What's ppm? Picometers?


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    Re: Chem help..... :O

    Post by The Banker on Wed Dec 30, 2009 5:32 pm

    part per million..
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    Re: Chem help..... :O

    Post by Ahmed on Wed Dec 30, 2009 5:33 pm

    Ahh, I see...unfortunately I didn't take it yet this year :S


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    Re: Chem help..... :O

    Post by The Banker on Wed Dec 30, 2009 5:34 pm

    kkz Smile
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    Re: Chem help..... :O

    Post by Ahmed on Wed Dec 30, 2009 5:34 pm

    Ask the kid in your avy, he might know Smile


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    Re: Chem help..... :O

    Post by The Banker on Wed Dec 30, 2009 5:36 pm

    u like?
    he's so cute i wanna eat da kid xD

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