OCR A Jan 2013 Paper 2 Q4 (with explained solutions) |

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OCR A Jan 2013 Paper 2 Q4

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F322/01 Question 4 (a) Mark Scheme January 2013 Guidance 1000 for first marking point if not calculated 24 IF there is an alternative answer, check to see if there is any ECF credit possible using working below. ALLOW 41.7 up to calculator value 41.6666667 correctly rounded. ALLOW ALLOW energy released per mole = 16.3 (cid:57) IGNORE () sign in the answer Common Incorrect answers 0.392 scores 2 marks 392000 scores 2 marks Marks Answer FIRST, CHECK THE ANSWER ON ANSWER LINE IF answer = 681 (kJ) award 3 marks Evidence of dividing 1000 by 24 Evidence of dividing by 3 and multiplying by 49 in the calculation energy released = 681 (kJ) (cid:57) (MUST BE TO 3 SIG FIGS) --------------------------------------------------------------------------- Alternative Working 3 moles = 72 dm3 (cid:57) So 1000 or 13.9 (cid:57) 72 Energy released = 13.949 = 681 (kJ) 12<br />
F322/01 Question 4 (b) Mark Scheme Marks Answer Ea enthalpy 3H2(g) + CO2(g) H CH3OH(g) + H2O(g) progress of reaction CH3OH and H2O added as product AND shown below the reactants (cid:57) H labelled with arrow pointing towards products or the product line if no products stated (cid:57) Ea labelled correctly AND above reactants (cid:57) 13 January 2013 Guidance IGNORE state symbols for the products IF there is no H labelled then ALLOW 49 only as an alternative label for H IF H is labelled then IGNORE any numerical value DO NOT ALLOW H ALLOW this arrow even if it has a small gap at the top and bottom i.e. does not quite reach reactant or product line ALLOW (+) 225 only as an alternative label for Ea ALLOW arrows at both ends of activation energy line The Ea line must point to maximum (or near to the maximum) on the curve ALLOW this line even if it has a small gap at the top and bottom ie does not quite reach the maximum or reactant line ALLOW AE or Ea for activation energy<br />
F322/01 Question (c) (d) (e) (f) Mark Scheme January 2013 Answer Marks 1 1 (+)49 (cid:57) (+)274 (cid:57) (equilibrium position shifts) to the left (cid:57) (Forward) reaction is exothermic OR reaction gives out heat OR reverse reaction is endothermic OR reverse reaction takes in heat (cid:57) The explanation mark is dependent on the correct shift of the equilibrium (equilibrium position) shifts to the left (cid:57) Right-hand side has fewer (gaseous) moles/molecules (cid:57) ORA The explanation mark is dependent on the correct shift of the equilibrium 14 DO NOT ALLOW 49 Guidance DO NOT ALLOW 274 ALLOW answer to (c) + 225 as ECF ALLOW favours the left, as alternative for shifts equilibrium to left Note: ALLOW suitable alternatives for to left, eg: towards CO2 / H2 OR towards reactants OR in backward direction OR in reverse direction OR decreases yield of CH3OH /products IGNORE responses in terms of rate ALLOW favours the left, as alternative for shifts equilibrium to left Note: ALLOW suitable alternatives for to left, eg: towards CO2 / H2 OR towards reactants OR in backward direction OR in reverse direction OR decreases yield of CH3OH /products IGNORE responses in terms of rate ALLOW four moles on the left and two moles on the right ALLOW more moles of reactants or fewer moles of products ASSUME goes the side with more gas molecules implies from equation that more molecules on the left OR goes to side with fewer gas molecules implies from equation that fewer molecules are on the right<br />
F322/01 Question (g) Mark Scheme January 2013 Marks Answer Adsorption of reactants OR adsorption of gases OR H2 and CO2 attached to surface (cid:57) Bonds weaken in reactants OR chemical reaction OR activation energy decreases (cid:57) Desorption of products OR desorption of H2O and CH3OH (cid:57) Guidance ALLOW CO2 and H2 (weakly) bonded to surface OR reactants bond to surface OR CO2 and H2 form temporary bonds with the catalyst DO NOT ALLOW absorption ALLOW bonds weaken in H2 OR bonds weaken in CO2 OR C=O bonds weaken OR bonds break and new bonds made in product OR H2O and CH3OH made ALLOW products leave the surface/catalyst OR H2O and CH3OH no longer bonded to surface/catalyst ALLOW deadsorption OR adsorb from for desorption ALLOW diffuse away for desorption Total 15 15<br />

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