4 Required practical 2 Measurement of an enthalpy change

 

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Oxford Textbook Pages : 80 - 81, 515 - 516

CGP Revision Guide Pages : 38

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Show Specification Ref : 3.1.4.2

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Question 1 / 5

AQA Jan 2013 Paper 1 Q5 section b answer all questions in the spaces provided do not write outside the box ammonia is used to make nitric acid hno by the ostwald process three reactions occur in this process reaction reaction reaction nh g o g no g h o g no g o g no g no g h o i hno aq no g a in one production run the gases formed in reaction occupied a total volume of m at c and kpa calculate the amount in moles of no produced give your answer to significant figures the gas constant r j k mol marks extra space wmp jan chem do not write outside the box b in another production run kg of ammonia gas were used in reaction and all of the no gas produced was used to make no gas in reaction b i calculate the amount in moles of ammonia in kg marks b ii calculate the mass of no formed from kg of ammonia in reaction assuming an yield give your answer in kilograms if you have been unable to calculate an answer for part b i you may assume a value of mol this is not the correct answer marks extra space question continues on the next page turn over wmp jan chem do not write outside the box c consider reaction in this process no g h o i hno aq no g calculate the concentration of nitric acid produced when mol of no is reacted with water and the solution is made up to cm marks extra space d suggest why a leak of no gas from the ostwald process will cause atmospheric pollution mark e give one reason why excess air is used in the ostwald process mark f ammonia reacts with nitric acid as shown in this equation nh hno nh no deduce the type of reaction occurring mark 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 Jan 2010 Paper 4 Q3 areas outside the box will not be scanned for marking propanone and iodine react in acidic conditions according to the following equation ch coch i ich coch hi a student studied the kinetics of this reaction using hydrochloric acid and a solution containing propanone and iodine from the results the following rate equation was deduced rate k ch coch h a give the overall order for this reaction mark b when the initial concentrations of the reactants were as shown in the table below the initial rate of reaction was found to be mol dm s ch coch i h initial concentration mol dm use these data to calculate a value for the rate constant k for the reaction and give its units calculation units marks c deduce how the initial rate of reaction changes when the concentration of iodine is doubled but the concentrations of propanone and of hydrochloric acid are unchanged mark wmp jan chem areas outside the box will not be scanned for marking d the following mechanism for the overall reaction has been proposed step ch coch h h c c ch oh step h c c ch oh ch h oh step step ch i oh ch i ich c o ch ich c o ich c ch h use the rate equation to suggest which of the four steps could be the rate determining step explain your answer rate determining step explanation marks e use your understanding of reaction mechanisms to predict a mechanism for step by adding one or more curly arrows as necessary to the structure of the carbocation below step h c c ch oh ch h oh mark turn over wmp jan chem
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Question 4 / 5

AQA Jan 2012 Paper 4 Q2 do not write outside the box at high temperatures and in the presence of a catalyst sulfur trioxide decomposes according to the following equation so g so g o g h kj mol a in an experiment mol of sulfur trioxide were placed in a container of volume dm and allowed to come to equilibrium at temperature t there were mol of oxygen in the equilibrium mixture a i calculate the amount in moles of sulfur trioxide and of sulfur dioxide in the equilibrium mixture amount of sulfur trioxide amount of sulfur dioxide marks a ii write an expression for the equilibrium constant kc for this equilibrium mark a iii deduce the units of kc for this equilibrium mark a iv calculate a value of kc for this equilibrium at temperature t if you were unable to complete the calculations in part a i you should assume that the amount of sulfur trioxide in the equilibrium mixture was mol and the amount of sulfur dioxide was mol these are not the correct values marks extra space wmp jan chem do not write outside the box b the experiment was repeated at the same temperature using the same amount of sulfur trioxide but in a larger container state the effect if any of this change on b i the amount in moles of oxygen in the new equilibrium mixture mark b ii the value of kc mark c the experiment was repeated in the original container but at temperature t the value of kc was smaller than the value at temperature t state which is the higher temperature t or t explain your answer higher temperature explanation marks extra space turn over wmp jan chem
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Question 5 / 5

AQA Jan 2012 Paper 4 Q4 do not write outside the box a this question involves calculations about two strong acids and one weak acid all measurements were carried out at oc a cm sample of mol dm hydrochloric acid was placed in a beaker and cm of distilled water were added calculate the ph of the new solution formed give your answer to decimal places marks extra space b hx is a weak monobasic acid b i write an expression for the acid dissociation constant ka for hx mark b ii the ph of a mol dm solution of hx is calculate a value for the acid dissociation constant ka of this acid give your answer to significant figures marks extra space wmp jan chem do not write outside the box c a cm sample of mol dm nitric acid was placed in a beaker and cm of mol dm aqueous sodium hydroxide were added calculate the ph of the solution formed give your answer to decimal places the ionic product of water kw mol dm at oc marks extra space turn over wmp jan chem
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