DP Chemistry (last assessment 2024)

Question 21M.2.hl.TZ2.7

Date	May 2021	Marks available	[Maximum mark: 6]	Reference code	21M.2.hl.TZ2.7
Level	hl	Paper	2	Time zone	TZ2
Command term	Determine, State, State and explain	Question number	7	Adapted from	N/A

[Maximum mark: 6]

21M.2.hl.TZ2.7

Consider the following equilibrium reaction:

2SO₂ (g) + O₂ (g) $⇌$ 2SO₃ (g)

(a)

State the equilibrium constant expression, K_c, for the reaction above.

[1]

Markscheme

«K_c = $\frac{{[{SO}_{3}]}^{2}}{{[{SO}_{2}]}^{2} [O_{2}]}$ » ✓

Square brackets required for the mark.

(b)

State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.

[3]

Markscheme

pressure decrease «due to larger volume» ✓

reaction shifts to side with more moles/molecules «of gas» ✓

reaction shifts left/towards reactants ✓

Award M3 only if M1 OR M2 awarded.

(c)

SO₂ (g), O₂(g) and SO₃(g) are mixed and allowed to reach equilibrium at 600 °C.

Determine the value of K_c at 600 °C.

[2]

Markscheme

[O₂] = 1.25 «mol dm⁻³» AND [SO₃] = 3.50 «mol dm⁻³» ✓

«K_c = $\frac{{[3.50]}^{2}}{{[1.50]}^{2} [1.25]}$ =» 4.36 ✓

Award [2] for correct final answer

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