AQA Jun 2015 Paper 2 Q4 (with explained solutions) |

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AQA Jun 2015 Paper 2 Q4

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do not write outside the box a hydrogen is produced in industry from methane and steam in a two stage process in the first stage carbon monoxide and hydrogen are formed the equation for this reaction is ch g h o g co g h g h kj mol a i use le chatelier s principle to state whether a high or low temperature should be used to obtain the highest possible equilibrium yield of hydrogen from this first stage explain your answer marks temperature explanation a ii le chatelier s principle suggests that a high pressure will produce a low yield of hydrogen in this first stage explain in terms of the behaviour of particles why a high operating pressure is used in industry marks wmp jun chem a iii a nickel catalyst is used in the first stage do not write outside the box explain why the catalyst is more effective when coated onto an unreactive honeycomb marks b the second stage is carried out in a separate reactor carbon monoxide is converted into carbon dioxide and more hydrogen is formed the equation for this reaction is co g h o g co g h g h kj mol use le chatelier s principle to state the effect if any of a decrease in the total pressure on the yield of hydrogen in this second stage explain your answer marks effect explanation turn over for the next question turn over wmp jun chem

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mark scheme a level chemistry chem june question a i mark marking guidance m high temperature or increase the temperature 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 m depends on correct m and must refer to temperature heat at high temperature the position of equilibrium shifts moves left to right to oppose the increase in temperature comments if m is incorrect ce for the clip if m is blank mark on and seek to credit the correct information in the text m depends on a correct statement for m for m the position of equilibrium shifts moves to absorb heat or to lower the temperature or to cool down the reaction of m the reaction gets to equilibrium faster in less time or produces a small yield faster in less time or increases the rate of reaction of attainment of equilibrium m high pressure leads to one of the following more particles molecules in a given volume particles they are closer together higher concentration of particles molecules and more collisions in a given time increased collision frequency a ii mark scheme a level chemistry chem june mark independently penalise m for reference to increased energy of the particles of mark scheme a level chemistry chem june m increase in more large r big ger surface area surface sites m increase in more successful productive effective collisions in a given time on the surface of the catalyst with the nickel m no effect none m requires a correct m equal same number amount of moles molecules particles on either side of the equation or moles molecules particles on the left and moles molecules particles on the right mark independently for m accept an increase in surface for m not simply more collisions ignore the chance or likelihood of collisions if m is incorrect ce for the clip if m is blank mark on and seek to credit the correct information in the text m depends on a correct statement for m in m not atoms of a iii b

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Topics to revise

AQA > Physical chemistry > Equilibrium AS >

1 Dynamic equilibrium and factors affecting equilibrium

AQA > Inorganic chemistry > Periodicity AS >

1 Periodicity

AQA > Physical chemistry > Equilibrium AS >

2 Industrial processes

AQA > Physical chemistry > Energetics and kinetics AS >

5 Kinetics

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

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