2 Calorimetry

 

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Oxford Textbook Pages : 77 - 80

CGP Revision Guide Pages : 39

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Show Specification Ref : 3.1.4.2

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Question 1 / 5

AQA Jan 2011 Paper 2 Q9 section b answer all questions in the spaces provided do not write outside the box a student devised an experiment to investigate the enthalpies of combustion of some alcohols the student chose the following series of primary alcohols name formula methanol ethanol propan ol butan ol pentan ol alcohol x heptan ol ch oh ch ch oh ch ch ch oh ch ch ch ch oh ch ch ch ch ch oh ch ch ch ch ch ch oh ch ch ch ch ch ch ch oh a i name alcohol x mark a ii state the general name of the type of series shown by these primary alcohols mark a iii draw the displayed formula of the position isomer of butan ol a iv using o to represent the oxidising agent write an equation for the oxidation of butan ol to form an aldehyde mark mark wmp jan chem a v draw the displayed formula of a functional group isomer of this aldehyde do not write outside the box b the student carried out a laboratory experiment to determine the enthalpy change when a sample of butan ol was burned the student found that the temperature of g of water increased by oc when x mol of pure butan ol was burned in air and the heat produced was used to warm the water mark use the student s results to calculate a value in kj mol for the enthalpy change when one mole of butan ol is burned the specific heat capacity of water is j k g marks extra space question continues on the next page turn over wmp jan chem c i give the meaning of the term standard enthalpy of combustion do not write outside the box marks extra space c ii use the standard enthalpy of formation data from the table and the equation for the combustion of butan ol to calculate a value for the standard enthalpy of combustion of butan ol ch ch ch ch oh i o g co g h o i h f kj mol ch ch ch ch oh i o g co g h o i marks extra space wmp jan chem do not write outside the box d the student repeated the experiment described in part b and obtained an experimental value for the enthalpy of combustion for each alcohol in this series these experimental values were then compared with calculated values from standard enthalpies of formation as shown in the graph below enthalpies of combustion values for a series of primary alcohols enthalpy of enthalpy of combustion combustion kj mol kj mol calculated experimental m of alcohol mr of alcohol d i in terms of bonds broken and bonds formed explain why the calculated values of enthalpies of combustion of these alcohols when plotted against mr follow a straight line marks extra space d ii give two reasons why the experimental values obtained by the student are lower than the calculated values using the enthalpy of formation data marks turn over wmp jan chem
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Question 2 / 5

AQA Jan 2013 Paper 2 Q4 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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Question 3 / 5

AQA Jun 2014 Paper 2 Q9 ethanol is an important fuel do not write outside the box a a dilute aqueous solution of ethanol can be produced by the fermentation of an aqueous solution of glucose it is claimed that the ethanol obtained from this solution is a carbon neutral biofuel write an equation for this fermentation reaction give two other essential conditions for this reaction to produce a good yield of ethanol name a process used to produce a much more concentrated solution of ethanol from a dilute aqueous solution state the meaning of the term carbon neutral in the context of this biofuel marks extra space question continues on the next page turn over wmp jun chem do not write outside the box b a student carried out a laboratory experiment to determine the enthalpy change when a sample of ethanol was burned the heat produced was used to warm some water in a copper calorimeter the student found that the temperature of g of water increased by c when mol of pure ethanol was burned in air use the student s results to calculate a value in kj mol for the enthalpy change when one mole of ethanol is burned the specific heat capacity of water is j k g deduce two reasons why the student s value for the standard enthalpy of combustion of ethanol is different from a data book value of kj mol marks extra space wmp jun chem do not write outside the box c mean bond enthalpies can be used to calculate enthalpies of reaction c i give the meaning of the term mean bond enthalpy marks c ii consider the mean bond enthalpy data in table table c h c c c o o o c o o h mean bond enthalpy kj mol to be calculated use the data in table and the equation shown to calculate a value for the bond enthalpy for the o o double bond in an oxygen molecule marks ch ch oh g o g co g h o g h kj mol end of questions wmp jun chem
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Question 4 / 5

AQA Jun 2015 Paper 2 Q7 do not write outside the box a propanone can be formed when glucose comes into contact with bacteria in the absence of air a i balance the following equation for this reaction of glucose to form propanone carbon dioxide and water c h o ch coch co h o a ii deduce the role of the bacteria in this reaction mark mark b propanone is also formed by the oxidation of propan ol b i write an equation for this reaction using o to represent the oxidising agent mark b ii state the class of alcohols to which propan ol belongs mark wmp jun chem do not write outside the box c a student determined a value for the enthalpy change when a sample of propanone was burned the heat produced was used to warm some water in a copper calorimeter the student found that the temperature of g of water increased by c when mol of pure propanone was burned in air use the student s results to calculate a value in kj mol for the enthalpy change when one mole of propanone is burned the specific heat capacity of water is j k g marks question continues on the next page turn over wmp jun chem d define the term standard enthalpy of combustion do not write outside the box marks e use the mean bond enthalpy data in table and the equation given below table to calculate a value for the standard enthalpy change when gaseous propanone is burned marks table c h c c c o o h c o o o mean bond enthalpy kj mol ch coch g o g co g h o g wmp jun chem do not write outside the box f suggest two reasons why the value obtained by the student in question c is different from the value calculated in question e marks reason reason turn over for the next question turn over wmp jun chem
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Question 5 / 5

AQA Jun 2014 Paper 5 Q2 table shows some enthalpy change and entropy change data do not write outside the box table h kj mol s j k mol agcl s agcl s agf s ag g ag g cl g ag aq cl aq ag aq f aq ag aq to be calculated a define the term enthalpy of hydration of an ion marks b use data from table to calculate a value for the enthalpy of hydration of the chloride ion marks c suggest why hydration of the chloride ion is an exothermic process marks wmp jun chem d silver chloride is insoluble in water at room temperature do not write outside the box use data from table to calculate the temperature at which the dissolving of silver chloride in water becomes feasible comment on the significance of this temperature value marks calculation of temperature significance of temperature value e when silver fluoride dissolves in water at c the free energy change is kj mol use this information and data from table to calculate a value with units for the entropy change when silver fluoride dissolves in water at c marks turn over wmp jun chem
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