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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
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