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    Guys I need help ASAP , I'm getting +76.5 for this question but the actual answer is -76.5 . Would really appreciate any help
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    This is my working:
    -60.4 + x = 52.3 + (-36.2)
    X=52.3 + (-36.2) + 60.4
    = +76.5
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    You have to do poducts-reactants since the enthalpy of formation is given. (you only do reactants - products when combustion data is given)

    Sum of the reactants= -36.2+52.3= + 16.1
    so -60.4- 16.1= -76.5 kJ mol^-1


    Hope this made sense
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    (Original post by Luj99)
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    Guys I need help ASAP , I'm getting +76.5 for this question but the actual answer is -76.5 . Would really appreciate any help
    There is just a sign difference. You must have the order wrong.

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    My order is correct guys
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    (Original post by Kvothe the arcane)
    There is just a sign difference. You must have the order wrong.

    I did exactly how you Did it , then I did 52.3+(-36.2)+60.4=+76.5
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    (Original post by Luj99)
    I did exactly how you Did it , then I did 52.3+(-36.2)+60.4=+76.5
    The two routes are going to be equal to each other due to Hess' law which states that the change of enthalpy in a chemical reaction (i.e. the heat of reaction at constant pressure) is independent of the pathway between the initial and final states.

    So \Delta H_f \ \text{ethane}+ \Delta H_f \ \text{Hydrogen bromide} + \Delta H_r=\Delta H_f \  \text{bromoethane}

    \therefore 52.3-36.2+ \Delta H_r = -60.4

    16.1+\Delta H_r = -60.4 \Rightarrow \Delta H_r = -60.4-16.1=-76.5\mathrm{Kjmol^{-1}}
 
 
 
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