Chemistry > AQA Questions and Marking Scheme > St. Paul's Co-educational College ( CHEM 000 )2020-HKDSE-CHEM_Mock_Exam_1_answers (updated, with MC (All)

St. Paul's Co-educational College ( CHEM 000 )2020-HKDSE-CHEM_Mock_Exam_1_answers (updated, with MC analysis)

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) S2O3 2–(aq) + 2H+(aq) → S(s) + SO2(g) + H2O(l) 1 (b) Rate  time taken for the 'blot out' of the cross 1 OR The time for blotting out the cross is inversely proportional to the rate of re... action. 1 (1) (c) When temperature increases, the average kinetic energy of reactant particles increases. This increases the collision frequency of reactant particles. Also, more particles possess sufficient energy to react / more particles with K.E. ⩾ Ea. Both causes the effective collision frequency to increase and hence the rate of reaction is increased. 1 1 (d) No. of mol of FeS2 = 598 / (55.8 + 32.1 × 2) = 4.98 mol No. of mol of SO2 formed = 4.98 × 2 = 9.96 mol Volume of SO2 = 9.96 × 24 = 239 dm3 1 1 [6] 13. (a) Initial concentration of NOCl(g) = 5.55 / 2.70 = 2.06 mol dm–3 Concentration (M) 2NOCl(g) 2NO(g) + Cl2(g) Initial 2.06 0 0 Change –0.68 +0.68 +0.34 Equilibrium 1.38 0.68 0.34 Kc = [NO(g)]2 [Cl2(g)] [NOCl(g)]2 = 0.682 × 0.34 / 1.382 = 0.0826 mol dm–3 (No mark will be awarded if the unit is incorrect.) 1 1 1 (b) (i) When the volume increases, pressure decreases. The equilibrium will counteract the decrease in pressure by shifting the equilibrium position to the right. It is because the product side / RHS has a higher no. of moles of gases. 1 (ii) 1 (iii) It does not change the equilibrium constant since Kc is only temperature-dependent. 1 (c) When the temperature is increased (from 25 o C to 100 o C), the value of Kc decreases. Since increasing temperature favours endothermic reaction, the value of Kc decreases indicating the the equilibrium position shifts to left. Hence, backward reaction is endothermic and forward reaction is exothermic. [Show More]

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