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);	3
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)	m(methanol) = (80.557 – 80.034) = 0.523 (g);
n(methanol) =  = 0.0163 (mol);	2
Award [2] for correct final answer.
 
(ii)	∆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);	3
Award [3] for correct final answer.
 
(iii)	∆H_c~~^O~~ =  / –25153 (J mol^–1);
= –25 (kJ mol^–1);	2
Award [2] for correct final answer.
Award [1] for (+)25 (kJ mol^–1).
 
(c)	(i)	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;	1
 
(ii)	not all heat produced transferred to water / heat lost to
surroundings/environment / OWTTE / incomplete combustion
(of methanol) / water forms as H_2O(l) instead of H_2O(g) ;	1
Do not allow just “heat lost”.
[12]

3.	D
[1]

4.	A
[1]

5.	(i)	nickel / platinum / palladium;
150–200 °C / heat;	2
Accept temperatures in this range.
Accept room temperature as an answer if platinum or palladium used.
 
(ii)	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
 
(iii)	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);	2
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)	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;	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
[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.	(i)	by definition ∆H_h~~^O~~ of elements (in their standard states) is zero / no
reaction involved / OWTTE;	1
 
(ii)	∆H = –104 – (+20.4);
= –124.4 (kJ mol^–1);	2
Award [1 max] for 124.4 (kJ mol^–1).
Award [2] for correct final answer.
 
(iii)	∆S = 270 – (267 + 131);
= –128 (J K mol^–1);	2
Award [1 max] for +128 (J K^–1 mol^–1).
Award [2] for correct final answer.
 
(iv)	∆G = ∆H – T∆S = –124.4 – ;
= –86.3 kJ mol^–1;	2
Units needed for the mark.
Award [2] for correct final answer.
Allow ECF if only one error in first marking point.

(v)	∆G = ∆H – T∆S = 0 / ∆H = T∆S;
T =  = 972 K / 699 °C;	2
Only penalize incorrect units for T and inconsistent ΔS value
once in (iv) and (v).
[9]

13.	B
[1]

14.	A
[1]

15.	A
[1]

16.	(i)	I:
atomization/sublimation (of Mg) / ∆H~~^O~~_atomization(Mg) / ∆H~~^O~~_sublimation(Mg);
	V:
enthalpy change of formation of (MgCl_2) / ∆H~~^O~~_formation(MgCl_2);	2
 
(ii)	Energy value for II:
+243;
	Energy value for III:
738 + 1451 = 2189;
	Energy value for IV:
2(–349);
∆H~~^O~~_lat(MgCl_2) = 642 + 148 + 243 + 2189 = (+)2252(KJ);	4
 
(iii)	theoretical value assumes ionic model;
experimental value greater due to (additional) covalent character;	2
 
(iv)	oxide greater charge;
oxide smaller radius;
Accept opposite arguments.	2
[10]

17.	(i)	c: atomization (enthalpy);
d: electron affinity;	2
 
(ii)	d and e;	1
 
(iii)	∆H_f = 90.0 + 418 + 112 + (–342) + (–670);
       = –392 kJ mol^–1;	2
 
(iv)	Ca^2+ is smaller than K^+ and Ca^2+ has more charge than K^+ / Ca^2+ 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]

18.	C
[1]

e;	1
 
(iii)	∆H_f = 90.0 + 418 + 112 + (–342) + (–670);
       = –392 kJ mol^–1;	2
 
(iv)	Ca^2+ is smaller than K^+ and Ca^2+ has more charge than K^+ / Ca^2+ 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]

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;	2
 
(ii)

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