AQA Jan 2013 Paper 2 Q4

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do not write outside the box a student used hess s law to determine a value for the enthalpy change that occurs when anhydrous copper ii sulfate is hydrated this enthalpy change was labelled hexp by the student in a scheme of reactions anhydrous copper ii sulfate water hexp hydrated copper ii sulfate h water h water copper ii sulfate solution a state hess s law mark b write a mathematical expression to show how hexp h and h are related to each other by hess s law mark c use the mathematical expression that you have written in part b and the data book values for the two enthalpy changes h and h shown to calculate a value for hexp h kj mol h kj mol mark wmp jan chem do not write outside the box d the student added mol of pure anhydrous copper ii sulfate to cm of deionised water in an open polystyrene cup an exothermic reaction occurred and the temperature of the water increased by c d i use these data to calculate the enthalpy change in kj mol for this reaction of copper ii sulfate this is the student value for h in this experiment you should assume that all of the heat released is used to raise the temperature of the g of water the specific heat capacity of water is j k g marks d ii suggest one reason why the student value for h calculated in part d i is less accurate than the data book value given in part c mark e suggest one reason why the value for hexp cannot be measured directly mark extra space turn over wmp jan chem

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