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

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AQA Jan 2012 Paper 2 Q2

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do not write outside the box ammonia is manufactured by the haber process in which the following equilibrium is established a give two features of a reaction at equilibrium n g h g nh g feature feature marks b explain why a catalyst has no effect on the position of an equilibrium marks extra space question continues on the next page turn over wmp jan chem do not write outside the box c the diagram shows how the equilibrium yield of ammonia varies with changes in pressure and temperature equilibrium yield of ammonia k k k pressure mpa c i use the diagram to state the effect of an increase in pressure at constant temperature on the yield of ammonia use le chatelier s principle to explain this effect effect on yield explanation marks extra space wmp jan chem do not write outside the box c ii use the diagram to state the effect of an increase in temperature at constant pressure on the yield of ammonia use le chatelier s principle to explain this effect effect on yield explanation marks extra space d at equilibrium with a pressure of mpa and a temperature of k the yield of ammonia is d i state why industry uses a temperature higher than k mark d ii state why industry uses a pressure lower than mpa do not include references to safety mark turn over wmp jan chem

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mark scheme general certificate of education a level chemistry unit chemistry in action january comments for m accept for concentration not equal concentrations and not concentration s is are the same not amount ignore dynamic and ignore speed ignore closed system it is possible to score both marks under the heading of a single feature if m is given as no effect no change then ce for clip ignore references to decrease in rate if m is given as decreases no effect no change then ce for clip but mark on from a blank ignore volumes particles atoms and species for m for m not simply to oppose the change for m credit the equilibrium shifts moves to lower decrease the pressure there must be a specific reference to the change that is opposed question a marking guidance in either order m concentrations of reactants and products remain or stay constant the same m forward rate reverse backward rate mark b m catalysts increase rate of speed up both forward and m increase in rate affect on rate speed is equal the same reverse backward reactions c i m the yield increases goes up gets more reactants or fewer moles molecules of gas on the right products or there are moles molecules of gas on the left and m there are more moles molecules of gas on the left of moles molecules on the right molecules m can only score m if m is correct the equilibrium shifts moves from left to right to oppose the increase in pressure or equilibrium shifts moves to the side with less moles c ii mark scheme general certificate of education a level chemistry unit chemistry in action january if m is given as increase no effect no change then ce for clip but mark on from a blank for m not simply to oppose the change for m credit the equilibrium shifts moves 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 credit correct reference to rate being too s low s lower at temperatures less than k ignore statements about the yield of ammonia not just less expensive alone not just less energy or saves energy alone credit correct qualified references to higher pressures ignore references to safety heat or reverse reaction is endothermic or takes in absorbs heat m the yield decreases goes down gets less m forward reaction is exothermic or gives out releases can only score m if m is correct the equilibrium shifts moves from right to left to oppose the increase in temperature higher rate of reaction or increase speed up the rate of reaction or gets to equilibrium faster quicker or faster or quicker rate speed of attainment of equilibrium d i must be comparative d ii less electrical pumping cost or use lower pressure equipment valves gaskets piping etc or uses less expensive equipment

Question 1 2 3 4 5 6 7 8 9 10

Topics to revise

AQA > Physical chemistry > Equilibrium AS >

1 Dynamic equilibrium and factors affecting equilibrium

AQA > Physical chemistry > Energetics and kinetics AS >

5 Kinetics

AQA > Physical chemistry > Equilibrium AS >

2 Industrial processes

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

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