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To calculate the enthalpy of a reaction using bond enthalpies you would have to add together all of the bond enthalpies of new bonds formed (which will be a negative value because formation of bonds releases energy) and add this value to the total of the bond enthalpies of all of the bonds broken (which will be a positive value because breaking a bond requires an input of energy). Personally, it helps me a little more to draw out the structures of the reactants and products to see exactly which bonds are broken and which ones are formed. For example, for part a, 3 carbon-carbon triple bonds (reactants) are broken to form 3 carbon-carbon single bonds and 3 carbon-carbon double bonds in the resulting hydrocarbon ring structure.
104781135 wrote:I'm not getting the correct answer for part A. I get a -369kJ/mol but the answer is -597kJ/mol? Can anyone help me with this please?
Never mind, I figured it out. C6H6 is benzene, and all of benzene's carbon bonds are resonance bonds, which have a different bond enthalpy than a single carbon bond or triple carbon bond.
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