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Given that a chlorine-oxygen bond in ClO2(g) has an enthalpy of 243kJ/mol , an oxygen-oxygen bond has an enthalpy of 498kJ/mol , and the standard enthalpy of formation of ClO2(g) is ΔH∘f=102.5kJ/mol, use Hess's law to calculate the value for the enthalpy of formation per mole of ClO(g).

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  • 5 years ago

    ...

    -------------- ------------------- ------> ΔHf = 102.5 kJ/mol

    -------------- ---> ΔHf = ?

    ½Cl2 + O2 --> ClO(g) + ½O2 --> ClO2

    .......... ............ --------------- ------> ΔHrx = Σ(bond energies)

    ΔHrx = Σ(bond energies)

    ΔHrx = Cl-O + 1/2(O=O) + -2(Cl-O)

    ΔHrx = 1/2(498 kJ) + -(243 kJ) = +6 kJ

    ΔHf(ClO2) = ΔHf(ClO) + ΔHrx

    ΔHf(ClO) = ΔHf(ClO2) - ΔHrx

    ΔHf(ClO) = 102.5kJ/mol - (+6 kJ/mol)

    ΔHf(ClO) = 96.5 kJ/mol

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