AQA Jan 2013 Paper 5 Q1

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section a answer all questions in the spaces provided do not write outside the box this question is about bond dissociation enthalpies and their use in the calculation of enthalpy changes a define bond dissociation enthalpy as applied to chlorine marks b explain why the enthalpy of atomisation of chlorine is exactly half the bond dissociation enthalpy of chlorine mark c the bond dissociation enthalpy for chlorine is kj mol and that for fluorine is kj mol the standard enthalpy of formation of clf g is kj mol c i write an equation including state symbols for the reaction that has an enthalpy change equal to the standard enthalpy of formation of gaseous clf mark wmp jan chem c ii calculate a value for the bond enthalpy of the cl f bond do not write outside the box marks c iii calculate the enthalpy of formation of gaseous chlorine trifluoride clf g use the bond enthalpy value that you obtained in part c ii if you have been unable to obtain an answer to part c ii you may assume that the cl f bond enthalpy is kj mol this is not the correct value marks c iv explain why the enthalpy of formation of clf g that you calculated in part c iii is likely to be different from a data book value mark d suggest why a value for the na cl bond enthalpy is not found in any data book mark turn over wmp jan chem

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