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Published byCorey Merritt Modified over 5 years ago
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Making bonds has the same value but opposite sign
Bond Enthalpies… Bond enthalpy is: The energy to BREAK bonds It is an ENDOTHERMIC process ΔH is therefore POSITIVE Making bonds has the same value but opposite sign
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Bond Enthalpies… In order to calculate the bond enthalpy of a compound we need to know the number of each type of bond.
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7 Cl H O H C=C-C-C-C OH H H H H Bond Enthalpies…
How many bond types are in the below compound? Cl H O H C=C-C-C-C OH H H H H 7
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Bond Enthalpies… Will the carbon – chlorine bond in the previous compound require the same amount of energy to break as the carbon – chlorine bond in: Cl No – but it isn’t possible to measure the enthalpy of EVERY bond. So we use averages
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Bond Enthalpies… Average Bond Enthalpy: The mean energy needed for 1 mole of a given type of gaseous bond to undergo homolytic fission
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Bond Enthalpies… Average Bond Enthalpy: The mean energy needed for 1 mole of a given type of gaseous bond to undergo homolytic fission
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Bond Enthalpies… Homolytic fission is simply the process where a bond is broken and each atom gains one electron to form a radical
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We can use the average bond enthalpies to calculate ΔH:
ΔH = Σ(reactants) - Σ(products) Σ(reactants) > Σ(products) = ENDO Σ(reactants) < Σ(products) = EXO
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Bond Enthalpies… When calculating the enthalpy change you must look at the type of enthalpy you are being asked for. e.g. ΔfHӨ requires only 1 mole of product to be formed
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