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1. A [1] 2. (a) amount of energy required to break bonds of reactants 3 × 413 + 358 + 464 + 1.5 × 498 (kJ mol–1) / 2808 (kJ mol–1); amount of energy released during bond formation of products 4 × 464 + 2 × 746 (kJ mol–1) / 3348 (kJ mol–1); ∆H = –540 (kJ mol–1); Award [3] for correct final answer. Award [2] for (+)540. If old Data Booklet is used accept answer: –535 (kJ mol–1) or award [2] for (+)535. (b) (i) (ii) (iii) m(methanol) = (80.557 – 80.034) = 0.523 (g); 0.523 g = 0.0163 (mol); n(methanol) = 1 32.05 g mol Award [2] for correct final answer. ∆T = (26.4 – 21.5) = 4.9 (K); q = (mc∆T =) 20.000 × 4.18 × 4.9 (J) / 20.000 × 4.18 × 4.9 × 10–3 (kJ); 0.41 (kJ); Award [3] for correct final answer. ∆HcO = (i) (ii) 2 3 0.41 (kJ) / –25153 (J mol–1); 0.0163 (mol) = –25 (kJ mol–1); Award [2] for correct final answer. Award [1] for (+)25 (kJ mol–1). (c) 3 bond enthalpies are average values/differ (slightly) from one compound to another (depending on the neighbouring atoms) / methanol is liquid not gas in the reaction; not all heat produced transferred to water / heat lost to surroundings/environment / OWTTE / incomplete combustion (of methanol) / water forms as H2O(l) instead of H2O(g) ; Do not allow just “heat lost”. 2 1 1 [12] IB Questionbank Chemistry 1 3. D [1] 4. A [1] 5. (i) (ii) (iii) nickel / platinum / palladium; 150–200 °C / heat; Accept temperatures in this range. Accept room temperature as an answer if platinum or palladium used. the enthalpy change when (one mole of) the gaseous bond is broken (or formed) / X–Y(g) → X(g) + Y(g) / X(g) + Y(g) → X–Y(g); averaged for the same bond in a number of similar compounds / OWTTE; 2 energy in: C=C + H–H and energy out: C–C + 2C–H; Accept energy in C–C + 6C–H + C=C + H–H and energy out 2C–C + 8C–H. ∆H = (612 + 436) – (347 + 826) = 1048 – 1173 / –125 (kJ mol–1); Award [2] for correct final answer. Award [1] for +125. If old Data Booklet values then allow: ∆H = 1048 – 1172 = –124 (kJ mol–1) (iv) 2 due to the relative strength of the C–C and 2C–H bonds compared to the C=C and H–H bonds / bonds in products stronger than bonds in reactants; 2 1 [7] 6. bonds broken: 4 N–H, N–N, O=O / +2220 (kJ mol–1); bonds formed: 1 N≡N, 4O–H / –2801(kJ mol–1); –581 (kJ mol–1); Award [3] for correct final answer. 3 [3] 7. D [1] 8. C IB Questionbank Chemistry 2 [1] 9. B [1] 10. D [1] 11. the reaction gives out (Gibbs Free) energy that can do work; ∆G for the reaction has a negative value; a reaction that occurs without adding energy (beyond that required to overcome energy barrier); 1 max [1] ˜Þ12. (ii) (iii) (iv) (i) by definition ∆HhO of elements (in their standard states) is zero / no reaction involved / OWTTE; 1 ∆H = –104 – (+20.4); = –124.4 (kJ mol–1); Award [1 max] for 124.4 (kJ mol–1). Award [2] for correct final answer. 2 ∆S = 270 – (267 + 131); = –128 (J K mol–1); Award [1 max] for +128 (J K–1 mol–1). Award [2] for correct final answer. 2 ∆G = ∆H – T∆S = –124.4 – (128 298) ; 1000 = –86.3 kJ mol–1; Units needed for the mark. Award [2] for correct final answer. Allow ECF if only one error in first marking point. IB Questionbank Chemistry 2 3 (v) ∆G = ∆H – T∆S = 0 / ∆H = T∆S; 124.4 T= = 972 K / 699 °C; 128 / 1000 Only penalize incorrect units for T and inconsistent ΔS value once in (iv) and (v). 2 [9] 13. B [1] 14. A [1] 15. A [1] 16. (i) I: atomization/sublimation (of Mg) / ∆HOatomization(Mg) / ∆HOsublimation(Mg); V: enthalpy change of formation of (MgCl2) / ∆HOformation(MgCl2); (ii) 2 Energy value for II: +243; Energy value for III: 738 + 1451 = 2189; (iii) (iv) Energy value for IV: 2(–349); ∆HOlat(MgCl2) = 642 + 148 + 243 + 2189 = (+)2252(KJ); 4 theoretical value assumes ionic model; experimental value greater due to (additional) covalent character; 2 oxide greater charge; oxide smaller radius; Accept opposite arguments. 2 [10] 17. (i) c: atomization (enthalpy); IB Questionbank Chemistry 4 d: electron affinity; 2 (ii) d and e; 1 (iii) ∆Hf = 90.0 + 418 + 112 + (–342) + (–670); = –392 kJ mol–1; 2 Ca2+ is smaller than K+ and Ca2+ has more charge than K+ / Ca2+ has a greater charge density; so the attractive forces between the ions are stronger; Do not accept “stronger ionic bonds” Award [1 max] if reference is made to atoms or molecules instead of ions. 2 (iv) [7] 18. C [1] e; 1 (iii) (iv) ∆Hf = 90.0 + 418 + 112 + (–342) + (–670); = –392 kJ mol–1; 2 Ca2+ is smaller than K+ and Ca2+ has more charge than K+ / Ca2+ has a greater charge density; so the attractive forces between the ions are stronger; Do not accept “stronger ionic bonds” Award [1 max] if reference is made to atoms or molecules instead of ions. 2 [7] 19. D [1] IB Questionbank Chemistry 5 20. (i) lattice enthalpy for a particular ionic compound is defined as ΔH for the process, MX(s) → M+(g) + X–(g); Accept definition for exothermic process electron affinity is the energy change that occurs when an electron is added to a gaseous atom or ion; (ii) 2 H f = –411 kJ mol –1 + Na(s) +108 kJ mol –1 12 Cl 2 (g) +121 kJ mol –1 Cl(g) Na(g) +494 kJ mol –1 Na+ (g) NaCl(s) –364 kJ mol –1 + – Cl (g) lattice enthalpy = –[(–411) – (+108) – (+494) – (+121) – (–364)] = 770 (kJ mol–1) Award [2] for all correct formulas in correct positions on cycle diagram. 1 incorrect or missing label award [1]. Award [1] for all correct values in correct positions on cycle diagram. calculation of lattice enthalpy of NaCl(s) = 770 (kJ mol–1); 4 Allow ECF. Accept alternative method e.g. energy level diagram. (iii) lattice/network/regular structure; each chloride ion is surrounded by six sodium ions and each sodium ion is surrounded by six chloride ions/6:6 coordination; 2 [8] IB Questionbank Chemistry 6