Edexcel Jun 2010 Paper 2 Q21 (with explained solutions) |

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Edexcel Jun 2010 Paper 2 Q21

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PMT 21 (a) In the catalytic converter of a car engines exhaust system, the following reaction occurs. 2NO(g) + 2CO(g) (cid:85) N2(g) + 2CO2(g) H = 745 kJ mol1 The temperature in a catalytic converter is high. (i) State the effect, if any, on the position of equilibrium if the temperature is lowered. Give a reason for your answer. (2) EffectReason(ii) The gases from the engine are not cooled before entering the converter. Explain why this is so. (2)(iii) State the effect, if any, on the position of equilibrium if the pressure on the reacting gases is increased. Give a reason for your answer. (2) EffectReason*N36390A01724* 17 Turn over<br />
(b) Nitrogen monoxide, NO, is formed when nitrate ions, NO3 reduced by silver metal. . (i) Calculate the oxidation number of nitrogen in NO and in NO3 , in acidic solution are In NO(ii) Balance the half-equation for the reduction of nitrate ions, NO3 In NO3 , in acidic solution. PMT (2) NO3+ H+ + eNO + H2O (iii) Write the half-equation for the oxidation of silver metal, Ag, to silver ions, Ag+. (iv) Hence deduce the full ionic equation for the reaction between silver metal and nitrate ions in acidic solution. State symbols are not required. (1) (1) (2) (Total for Question 21 = 12 marks) TOTAL FOR SECTION B = 38 MARKS 18 *N36390A01824*<br />

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Acceptable Answers Reject Mark Equilibrium shifts to left will score (0) for (a)(i) Mark the two points independently, subject to the constraint in Reject column Effect: (Equilibrium) shifts to the right (1) ALLOW: favours forward reaction / increase the amount of product / increase the yield (of product) Reason: Exothermic (in forward direction) (1) NOTE: Just (equilibrium) shifts in the exothermic direction scores (1) Acceptable Answers Reject Mark First mark: Activation energy for the reaction is too high / (if cooled) molecules would not have enough energy to react / few(er) molecules have the required Ea/more molecules have energyEa at higher temperatures OR not (technologically) feasible to cool the gases before they enter the converter/costly to cool the gases Second mark: (cooling the gases would make) the rate (too) slow /rate is faster if the temperature is high (so the gases are not cooled) Question Number 21(a)(i) Question Number 21(a)(ii) (1) (1) Cooling the gases decreases the yield (of products) /an incorrect Le Chatelier argument 6CH0201 1006<br />
Question Number 21(a)(iii) Question Number 21(b)(i) Question Number 21(b)(ii) Acceptable Answers Reject Mark Mark the two points independently, subject to the constraint in Reject column Effect: (Equilibrium) shifts to the right ALLOW: favours forward reaction / increase the amount of product / increase the yield of product Reason: Shifts / moves in the direction of fewer (moles of gas) molecules ALLOW shifts in direction of fewer moles (of gas molecules) IGNORE effect on the rate Equilibrium shifts to left will score (0) for (a)(iii)fewer atoms (1) (1) Acceptable Answers Reject Mark ): +5 / 5+ (1) (In NO): +2 / 2+ (1) (In NO3 NOTE: (In NO): Just 2 AND (In NO3 ): Just 5 scores (1) Acceptable Answers Reject Mark+ 4H+ + 3eNO + 2H2O NO3 ACCEPT multiples 6CH0201 1006<br />
Question Number 21(b)(iii) Question Number 21(b)(iv) Acceptable Answers Reject Mark AgAg+ + e() / Age()Ag+ ACCEPT multiples IGNORE state symbols, even if incorrect Ag + e (cid:198) Ag+ Acceptable Answers Reject Mark 3Ag + NO3+ 4H+ (cid:198) 3Ag+ + NO + 2H2O (2) (1) for multiplication of the silver half-equation by three or cq multiple from (b)(ii) (1) for rest of equation correct NOTE: Equation must be completely correct for the second mark. IGNORE state symbols, even if incorrect if any e are left in the final equation, second mark cannot be scored 6CH0201 1006<br />

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