AQA Jun 2012 Paper 2 Q2 (with explained solutions) |

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AQA Jun 2012 Paper 2 Q2

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do not write outside the box methanol ch oh is an important fuel that can be synthesised from carbon dioxide a the table shows some standard enthalpies of formation co g h g ch oh g h o g hf kj mol a i use these standard enthalpies of formation to calculate a value for the standard enthalpy change of this synthesis co g h g ch oh g h o g marks extra space a ii state why the standard enthalpy of formation for hydrogen gas is zero mark wmp jun chem b state and explain what happens to the yield of methanol when the total pressure is increased in this synthesis do not write outside the box co g h g ch oh g h o g effect on yield explanation marks extra space c the hydrogen required for this synthesis is formed from methane and steam in a reversible reaction the equation for this reaction is shown below ch g h o g co g h g h kj mol state and explain what happens to the yield of hydrogen in this reaction when the temperature is increased effect on yield explanation marks extra space question continues on the next page turn over wmp jun chem do not write outside the box d the methanol produced by this synthesis has been described as a carbon neutral fuel d i state the meaning of the term carbon neutral mark extra space d ii write an equation for the complete combustion of methanol mark d iii the equation for the synthesis of methanol is shown below co g h g ch oh g h o g use this equation and your answer to part d ii to deduce an equation to represent the overall chemical change that occurs when methanol behaves as a carbon neutral fuel equation mark wmp jun chem do not write outside the box e a student carried out an experiment to determine the enthalpy change when a sample of methanol was burned the student found that the temperature of g of water increased by oc when mol of methanol was burned in air and the heat produced was used to warm the water use the student s results to calculate a value in kj mol for the enthalpy change when one mole of methanol was burned the specific heat capacity of water is j k g marks extra space turn over for the next question turn over wmp jun chem

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mark scheme general certificate of education a level chemistry unit chemistry in action june mark comments correct answer gains full marks credit mark only for kj mol for other incorrect or incomplete answers proceed as follows check for an arithmetic error ae which is either a transposition error or an incorrect multiplication this would score marks m and m if no ae check for a correct method this requires either correct cycle of balanced equations with c h and o or a clear statement of m which could be in words and scores only m ignore reference to standard state question marking guidance a i m could be scored by a correct mathematical expression which must have all h symbols and the or sum m hr hf products hf reactants or a correct cycle of balanced equations with c h and o m hr hr hr m kj mol award mark only for this also scores m a ii it is an element elemental or by definition mark scheme general certificate of education a level chemistry unit chemistry in action june b m the yield increases goes up gets more m there are more moles molecules of gas on the left of reactants or fewer moles molecules of gas on the right products or there are moles molecules of gas on the left and moles molecules on the right or equilibrium shifts moves to the side with less moles molecules m can only score m if m is correct the position of equilibrium shifts moves from left to right to oppose the increase in pressure if m is given as decreases no effect no change then ce for clip but mark on only m and m from a blank m ignore volumes particles atoms and species for m for m not simply to oppose the change for m credit the equilibrium shifts moves to right to lower decrease the pressure there must be a specific reference to the change that is opposed c mark scheme general certificate of education a level chemistry unit chemistry in action june if m is given as decrease no effect no change then ce for clip but mark on only m and m from a blank m for m not simply to oppose the change for m credit the position of equilibrium shifts moves qol to absorb the heat or to cool the reaction or to lower the temperature there must be a specific reference to the change that is opposed the idea that the carbon co given out equals the carbon co that was taken in from the atmosphere ignore state symbols accept multiples m yield increases goes up m the forward reaction to the right is endothermic or takes in absorbs heat or the reverse reaction to the left is exothermic or gives out releases heat can only score m if m is correct m the position of equilibrium shifts moves from left to right to oppose the increase in temperature qol d i an activity which has no net overall annual carbon emissions to the atmosphere or an activity which has no net overall annual greenhouse gas emissions to the atmosphere or there is no change in the total amount level of carbon dioxide co carbon greenhouse gas present in the atmosphere d ii ch oh o co h o mark scheme general certificate of education a level chemistry unit chemistry in action june d iii h o h o or h o h o e m q m c t or q x x m j or kj or kj or kj also scores m m using mol or gains marks therefore h kjmol or ignore state symbols accept multiples extra species must be crossed through award full marks for correct answer ignore the case for each letter penalise m only if correct numerical answer but sign is incorrect gains marks penalise m for arithmetic error and mark on in m do not penalise incorrect cases in the formula if t score q m c t only if c leads to penalise m only and mark on for m ignore incorrect units

Question 1 2 3 4 5 6 7 8 9

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 > Inorganic chemistry > Periodicity AS >

1 Periodicity

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

AQA > Organic Chemistry > Alkanes AS >

3 Combustion

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