Gh0strid3r
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How to calculate heat transfer using bond energies
(IGCSE)/ olevels
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username2752874
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(Original post by Gh0strid3r)
How to calculate heat transfer using bond energies
(IGCSE)/ olevels
Use the formula:

Enthalpy Change (or heat transfer) = Energy of the bonds broken - Energy of the bonds formed

Remember, bond breaking is positive while bond forming is negative
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Sonia2598
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Is there a question for it?
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Gh0strid3r
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Gh0strid3r
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(Original post by Sonia2598)
Is there a question for it?
Yes please the question is posted can u help
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Sonia2598
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So you do sum of energy required to break bonds which is the reactants minus sum of energy required to form bonds which is the products

So 678-862= -184KJ
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gingembread
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Overall energy change = (energy required to break bonds) - (energy released by forming bonds).

So, if you calculate the energy needed to break the H-H and the Cl-Cl bond using the data in the table, and subtract the energy released by forming two H-Cl bonds, you'll get the overall energy change.

Exothermic reactions are when energy is released to the surroundings, so the energy released by breaking bonds is greater than the energy used to break them. You can prove this by getting an overall energy change that's negative from this calculation. (:
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