O-LevelChemistryRates of Reaction5070/22 · May/June 2022 · Q57 Marks

Ethanol is manufactured by the reaction between ethene and steam. The conditions used are 300°C, a high pressure and a phosphoric acid catalyst. (a) The reaction between ethene and steam is reversible. The forward reaction is exothermic. C2H4(g) + H2O(g) ⇌ C2H5OH(g) An equilibrium mixture is formed when the reversible reaction happens in a closed system.

(a)(i)Predict what happens to the amount of ethanol in the equilibrium mixture if the temperature is decreased and the pressure remains constant. Explain your answer. prediction explanation[2]
(a)(ii)Predict what happens to the amount of ethanol in the equilibrium mixture if the pressure is decreased and the temperature remains constant. Explain your answer. prediction explanation[2]
(b)Describe the manufacture of aqueous ethanol by the fermentation of glucose. Include the equation and the essential conditions needed for this fermentation.[3]

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[1] more ethanol
[1] (equilibrium shifts to the right) to release energy / to release heat
[1] less ethanol
[1] (position of equilibrium shifts to the left) more of moles of gas on reactant side of equation / less moles of gas on product side
[1] C6H12O6 → 2C2H5OH + 2CO2
[1] presence of yeast / enzyme
[1] presence of water
[1] quoted temperature between 15 and 45 (°C) inclusive
[1] absence of oxygen

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.