DP Chemistry (first assessment 2025)

Question SPM.2.HL.TZ0.3

Date	May Specimen-2023	Marks available	[Maximum mark: 13]	Reference code	SPM.2.HL.TZ0.3
Level	HL	Paper	2	Time zone	TZ0
Command term	Calculate, Compare, Complete, Deduce, Determine, Draw, Sketch, State, Suggest	Question number	3	Adapted from	N/A

[Maximum mark: 13]

SPM.2.HL.TZ0.3

The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.

(a)

The diagram represents a cell in such a battery delivering a current. Complete the half-equations on the diagram and identify the species moving between the electrodes.

[3]

Markscheme

(b)

The discharge of the lithium-ion battery is a spontaneous chemical reaction producing a potential difference and an increase in temperature.

(b.i)

Deduce the signs of the following:

$Δ$ H_discharge: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E_cell: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

$Δ$ G_discharge: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[1]

Markscheme

$Δ$ H_discharge: negative AND

E_cell: positive AND

$Δ$ G_discharge: negative ✔

(b.ii)

The lithium-ion battery can be recharged by reversing the reactions at each electrode. Compare the absolute value of $Δ$ G_recharge and $Δ$ G_discharge.

[1]

Markscheme

$Δ$ G_recharge > $Δ$ G_{discharge ✔}

(c)

In a simulation, equal masses of potassium and lithium are added to water and the time taken for the metals to fully react is recorded. Five different increasing masses of each metal are used, and the reaction is timed.

(c.i)

Sketch the graphs on the axes to show the expected results of this experiment.

[2]

Markscheme

separate curves/lines for Li and K sketched AND both increasing ✔
steeper gradient for Li
OR
curve/line for Li higher ✔

(c.ii)

Suggest a reason why comparing the time for complete reaction of equal masses is not a valid measure of reactivity.

[1]

Markscheme

equal masses «of different substances» do not contain equal amounts/moles ✔

(c.iii)

Lithium carbide, Li₂C₂, is one of many compounds of lithium and carbon. Determine the percentage covalent character and bonding type in this compound by using sections 9 and 17 of the data booklet.

[2]

Markscheme

«Avg electronegativity = 1.8
$Δ$ electronegativity = 1.6»
% covalent character = 45-55 ✔
ionic ✔

(c.iv)

Calculate the Gibbs energy of formation, $Δ$ G_f^⦵, in kJ mol^{$-$ 1}, for Li₂C₂ at 298.15 K. Use the data provided and section 1 of the data booklet.

$Δ$ H_f^⦵ Li₂C_{2 solid} = $-$ 62 kJ mol^{$-$ 1}
$Δ$ S_f^⦵ Li₂C₂ _solid = $-$ 11 J mol^{$-$ 1} K^{$-$ 1}

[1]

Markscheme

« $Δ$ G^⦵ = $Δ$ H^⦵ $-$ T $Δ$ S^⦵ = $-$ 62 $-$ 298 × $-$ 0.011 =»
$-$ 59 «kJ mol^_$-$1» ✔

(c.v)

Draw the Lewis formula of the anion in the salt Li₂C₂.

[1]

Markscheme

[:C≡C:]^{2 $-$}

2 $-$ charge ✔

:C≡C: ✔

(c.vi)

State the type of hybridization shown by the carbon atoms in the anion.

[1]

Markscheme

sp ✔

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