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OCR A Jun 2017 Paper 1 Q23
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![18 23 Methanol can be prepared industrially by reacting carbon monoxide with hydrogen in the presence of a copper catalyst. This is a reversible reaction. CO(g) + 2H2(g) CH3OH(g) (a) Using the Boltzmann distribution model, explain why the rate of a reaction increases in the presence of a catalyst. You are provided with the axes below, which should be labelled.[4]<br />
19 (b) The reaction for the production of methanol in the presence of the copper catalyst is carried out at 200300 C. Explain why use of the catalyst reduces energy demand and benefits the environment.[2] (c) A chemist investigates the equilibrium that produces methanol: CO(g) + 2H2(g) CH3OH(g) The chemist mixes CO(g) with H2(g) and leaves the mixture to react until equilibrium is reached. The equilibrium mixture is analysed and found to contain the following concentrations. Substance Concentration /mol dm3 CO(g) H2(g) CH3OH(g) 0.310 0.240 0.260 Calculate the numerical value of Kc for this equilibrium. Give your answer to an appropriate number of significant figures. Kc =dm2 mol6 [2]<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_QP_-_Paper_1_OCR_Chemistry_A_AS-Level_23-0.jpg)
![H032/01 Question Answer nucleus) (cid:57)(cid:3) (c) (iv) Sub-shells Mg electron is removed from (3)s AND Al electron is removed from (3)p (cid:57) Energy levels Al electron has a higher energy OR (3)p has higher energy than (3)s (cid:57) Mark Scheme Marks June 2017 Guidance IGNORE held for attracted, e.g. IGNORE held more strongly IGNORE number before s and p e.g. ALLOW (2)s and (2)p ALLOW response implying that orbitals/sub-shell changes from s to p IGNORE comments about distance from nucleus IGNORE less energy to remove DO NOT ALLOW unpaired electron removed more easily (ORA) Total 16 Question 23 (a) Answer Marks Correct drawing of Boltzmann distribution Curve starts within two small squares of origin AND not touching the x axis at high energy (cid:57) axes labels: y: (number of) molecules/particles 10 Guidance FULL ANNOTATIONS WITH TICKS, CROSSES, CON, etc MUST BE USED IGNORE a slight inflexion on the curve DO NOT ALLOW two curves Confusion with effect of temperature<br />
H032/01 Question (b) (c) Answer AND x: (kinetic) energy (cid:57) Catalyst and activation energy Catalyst provides a lower activation energy OR Ec shown below Ea on Boltzmann distribution (cid:57) More molecules/particles/collisions have energy above activation energy (with catalyst) OR greater area under curve above activation energy (cid:57) Two max (cid:57)(cid:57) from: (cid:120) Lower temperatures/less heat/less thermal energy (cid:120) Less fossil fuels/oil/coal/gas/non-renewable fuels (cid:120) Reduces CO2 emissions FIRST, CHECK THE ANSWER ON ANSWER LINE IF answer = 14.6 (dm2 mol-6) award 2 marks -------------------------------------------------------------------- Kc expression 0.26 (Kc = ) [CH3OH] [CO] [H2]2 OR 0.31 0.242 OR 14.56(cid:57) Mark Scheme June 2017 Guidance DO NOT ALLOW atoms as y-axis label DO NOT ALLOW enthalpy for x-axis label ALLOW more molecules have enough energy to react IF y axis labelled as atoms ALLOW ECF for atoms (instead of molecules/particles) IGNORE (more) successful collisions IGNORE response implying more collisions (confusion with effect of greater temperature) IGNORE lower pressures OR less energy (in question) IGNORE just less fuel IGNORE less global warming IGNORE less greenhouse gases, less CO, less NO CO2 required FULL ANNOTATIONS MUST BE USED -------------------------------------------------------------------------- IF there is an alternative answer, check to see if there is any ECF credit possible using working below. ------------------------------------------------------------- ALLOW calculated value 14.5609319 correctly rounded to 3 or more SF for 1st marking point ALLOW ECF to 3 SF ONLY from inverted Kc expression Marks 11<br />
Answer Mark Scheme Marks Guidance June 2017 H032/01 Question Answer to 3 SF 14.6 (dm6 mol2) (cid:57) (cid:111) 0.0687 DO NOT ALLOW [CH3OH] [CO] + [H2]2 = 0.707 (no marks) Total 12<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_MS_-_Paper_1_OCR_Chemistry_A_AS-Level_23-0.jpg)
