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In calculating using bond enthalpies, the basic equation is enthalpy of rxn = bonds broken(reactant side) - bonds formed(product side). I find it easier to see exactly which bonds are broken if you draw out the structure of each of the molecules. Once you've done that, you can see that a C-I and H-O bond broke on the reactant side in order to form a C-O and H-I bond on the product side. That means deltaHrxn = [deltaH(C-I) + deltaH(H-O)] - [deltaH(C-O) - deltaH(H-I)]. Then, you can plug in the values provided to get deltaH(C-O).
Jata_Kavya_3A wrote:for every question with bond enthalpies vs enthalpies of formation, will the question specify what they want?
The question usually specifies it. The pattern I have encountered is that when they ask for bond enthalpies, they generally come with a table of bonds (H-O, C-C, etc). and when they want enthalpies of formation, the delta Hf is usually given for the molecules.
Hello, just to add on to the questions here, for 2 &3 part D, how do you know to ADD the summation of broken bonds to the summation of formed bonds. Usually the equation is summation of delta-H (broken bonds) minus the summation of delta-H (formed bonds)? And I also asks this because the two formed bonds are C-O and H-I, which releases energy, (so I am thinking of negative energy value), but the answer is +360kJ/mol.
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