AQA Jun 2015 Paper 5 Q2

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do not write outside the box table contains some bond enthalpy data bond bond enthalpy kj mol table h h o o h o a the value for the h o bond enthalpy in table is a mean bond enthalpy state the meaning of the term mean bond enthalpy for the h o bond marks b use the bond enthalpies in table to calculate a value for the enthalpy of formation of water in the gas phase marks wmp jun chem do not write outside the box c the standard enthalpy of combustion of hydrogen forming water in the gas phase is almost the same as the correct answer to question b c i suggest one reason why you would expect the standard enthalpy of combustion of hydrogen to be the same as the answer to question b mark c ii suggest one reason why you would expect the standard enthalpy of combustion of hydrogen to differ slightly from the answer to question b mark turn over for the next question turn over wmp jun chem

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