AQA Jun 2010 Paper 5 Q6 (with explained solutions) |

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AQA Jun 2010 Paper 5 Q6

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section b answer all questions in the spaces provided do not write outside the box methanol can be regarded as a carbon neutral fuel because it can be synthesised from carbon dioxide as shown in the equation below co g h g ch oh g h o g standard enthalpy of formation and standard entropy data for the starting materials and products are shown in the following table kj mol hf s j k mol co g h g ch oh g h o g a calculate the standard enthalpy change for this reaction marks b calculate the standard entropy change for this reaction marks wmp jun chem do not write outside the box c use your answers to parts a and b to explain why this reaction is not feasible at high temperatures calculate the temperature at which the reaction becomes feasible suggest why the industrial process is carried out at a higher temperature than you have calculated if you have been unable to calculate values for h and s you may assume that they are kj mol and j k mol respectively these are not the correct values marks extra space question continues on the next page turn over wmp jun chem d write an equation for the complete combustion of methanol use your equation to explain why the combustion reaction in the gas phase is feasible at all temperatures do not write outside the box marks extra space e give one reason why methanol synthesised from carbon dioxide and hydrogen may not be a carbon neutral fuel mark wmp jun chem do not write outside the box turn over for the next question do not write on this page answer in the spaces provided turn over wmp jun chem

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q part sub part a b c marking guidance h hf products hf reactants kj mol s s products s reactants x j k mol g h t s s is negative so at high temp t s is positive and greater than h large so g limiting condition g so t h s k reaction is too slow at this temperature to speed up the reaction chemistry aqa gce mark scheme june series mark comments kj mol mark units not required wrong units lose mark mark units not required wrong units lose mark if use g not g penalise m but not m and m do not award m or m if positive s value used independent mark unless positive s value used allow if used given values do not award m if t ve or if m should give t ve d co h o ch oh o mol give mol gases therefore s is positive entropy increases combustion exothermic so h ve so h t s and hence g always negative less than zero e co co ch may be produced during h manufacture building the plant transport operating the plant chemistry aqa gce mark scheme june series allow multiples ignore state symbols do not allow equation for wrong compound but mark on provided number of moles increases or stays the same if no equation or equation that gives a decrease in the number of moles ce allow statement increase in number of moles molecules if numerical values given they must match the equation in m ignore the effect of incorrect state symbols on the number of moles of particles unless used correctly if correct deduction from wrong equation is s or s very small must say h ve allow g instead of g can score out of marks if equation wrong but leads to increase or no change in number of moles m dependent on m note if equation wrong and there is an incorrect deduction about the change in number of moles ce

Question 1 2 3 4 5 6 7

Topics to revise

AQA > Physical chemistry > Equilibrium AS >

1 Dynamic equilibrium and factors affecting equilibrium

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

AQA > Physical chemistry > Energetics and kinetics AS >

5 Kinetics

AQA > Inorganic chemistry > Periodicity AS >

1 Periodicity

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

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