A-LevelChemistryChemical energetics9701/42 · May/June 2023 · Q312 Marks

Table 3.2 shows some energy changes. [Table 3.2]

(a)Complete Table 3.1 by placing one tick (✔) in each row to indicate the sign of each type of energy change under standard conditions. [Table 3.1][1]
(b)Define standard enthalpy change of atomisation.[2]
(c)Calculate the lattice energy, ΔHlatt, of Ag2O(s) using relevant data from Table 3.2. It may be helpful to draw a labelled energy cycle. Show your working. ΔHlatt of Ag2O(s) =[3]
(d)Suggest the trend in the magnitude of the lattice energies of the silver compounds Ag2S, Ag2O and Ag2Se. Explain your answer. least exothermic most exothermic[2]
(e)(i)Silver sulfite, Ag2SO3(s), is sparingly soluble in water. Give an expression for the solubility product, Ksp, of Ag2SO3. Ksp =[1]
(e)(ii)Calculate the equilibrium concentration of Ag+ in a saturated solution of Ag2SO3 at 298 K. [Ksp: Ag2SO3, 1.50 × 10-14 mol³ dm-9 at 298K] [Ag+] =[1]
(f)The standard enthalpy change of solution, ΔH°sol, of AgNO3(s) in water is +22.6kJmol−1. Suggest how the feasibility of dissolving AgNO3(s) in water changes with temperature. Explain your answer.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] Table 3.1 completed with ticks: bond energy (always positive), enthalpy change of atomisation (always positive), enthalpy change of formation (can be either negative or positive)
[1] M1 (enthalpy change) when one mole of gaseous atoms is produced IGNORE energy released
[1] M2 from its element(s) in its standard state / standard conditions / 298 K AND 1 atm
[1] M1 use of correct six numbers only –31 / 285/731/-141/798/496
[1] M2 2 x used correctly with Ag (2 × 285 (570) and 2 × 731 (1462)) AND 0.5 with O=O(496 (248))
[1] M3 correct signs and evaluation: -31 = (2 × 285) + (2 × 731) + (−141) + (798) + x + (0.5 × 496); x = -2968 kJ mol-1
[1] Ag2Se least exothermic, Ag2S, Ag2O most exothermic OWTTE
[1] charge density of anion decreases down the group ORA / radius/size of anion increases down the group / Se²- largest radius / O²– smallest radius / O has smallest ionic radius
[1] less attraction between the ions / ionic bond gets weaker (with Ag2Se) ORA
[1] (Ksp =) [Ag+]2[SO32-]
[1] x = 3√1.5 × 10–14/4 = 1.55 × 10-5 (mol dm-³); [Ag+] = 1.55 × 10–5 × 2 = 3.11 × 10–5(mol dm-³) min 2sf ecf (e)(i)
[1] feasibility / it increases as temperature increases ORA
[1] AS is positive / AS is >0 / entropy change is positive (and ∆H is positive) OR -TAS becomes more negative / TAS becomes more positive
[1] as AG becomes / is negative / AG < 0

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.