When iron is heated with steam in a sealed container, an equilibrium mixture is obtained. 3Fe(s) + 4H2O(g) ⇌ 4H2(g) + Fe3O4(s) ΔH = +35 kJ/mol

Mark scheme

Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.

1. [1] B9 (a) heat taken in / heat absorbed / heat energy taken in / heat energy absorbed (1)
2. [1] (b) Reaction rate increases (1)
3. [1] (b) Particles have more energy / particles moving faster / particles have more (kinetic) energy (1) More particles have energy above activation energy / more effective collisions / more successful collisions / more energetic collisions / more fruitful collisions (1)
4. [1] (c) Position of equilibrium does not change (1)
5. [1] (c) Same number moles of gas on both sides / same number of gas molecules on both sides / same volume of gas on both sides (1)
6. [1] (d) Moles of iron = 2.80/56 = 0.05 (1) (mark for working or correct answer)
7. [1] (d) Moles of Fe3O4 = 0.05/3 = 0.01667 (1) (mark for working or correct answer)
8. [1] (d) Mass of Fe3O4 = (0.01667 × 232) = 3.87g (1)
9. [1] (d) OR 168 g of Fe makes 232 g of Fe3O4 (1) ALLOW: Mr = 232
10. [1] (d) OR 2.8 g of Fe makes 232/168 × 2.8 (1)
11. [1] (d) OR Mass = 3.867 (1)
12. [1] (e) NOTE: must be reference to zinc somewhere in the answer. If not max 1 mark. Zinc coating / barrier / layer / covering (1) Stops water getting to iron / stops oxygen getting to iron (1)
13. [1] (e) OR Zinc is more reactive / zinc is above iron in the reactivity series / zinc more likely to be oxidised (1)
14. [1] (e) Zinc reacts in preference to iron (1)