Chemistry · Oct / Nov 2025 · Paper 41 · Question 4
0620
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The question as text
Gaseous sulfur tetrafluoride, SF4 , reacts with steam in a reversible reaction. SF4(g) + 2H2O(g) SO2(g) + 4HF(g) ΔH = –54 kJ / mol
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4(a)[4]
M1 energy level of products below energy level of reactants
M2 label of SO2(g) + 4HF(g) on product line
M3 upward arrow labelled Ea from energy level of reactants to the highest point of the curve
M4 one downward arrow labelled ΔH
AND
energy change starting from energy level of reactants and finishing at energy level of products
4(b)[4]
M1 = (4 × S–F) + (4 × O–H) = (4 × 330) + (4 × 460) = 3160
M2 bond energy of products – 3160 = –54
= 3160 – (–54) = 3214
M3 (2 × S=O) + (4 × H–F) = 3214 therefore 2 × S=O = 3214 – (4 × 570) = 934
M4 S=O = M3 ‣ 2 = 934 ‣ 2 = 467
4(c)[5]
increased temperature:
M1 (position of) equilibrium moves to left hand side
M2 reaction is exothermic
increased pressure:
M3 (position of) equilibrium moves to left hand side
M4 less (gaseous) moles on left hand side
M5 no change / catalyst does not affect position of equilibrium
4(d)[3]
M1 kinetic energy of particles decreases
M2 frequency of collisions between particles decreases
M3 lower percentage/proportion/fraction of collisions / particles have energy greater than / equal to activation energy
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