Question Constellation Sign up for free AQA · GCSE · Chemistry · Higher
Industrial equilibrium pressure compromise
The equation for the reaction is:
In industry, the reaction is done at 450 °C and atmospheric pressure. Under these conditions the yield of sulfur trioxide is 86%.
Suggest two reasons why a higher pressure is not used.
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Marking points
- 1 Gives one valid reason from the official list: yield already high, energy cost, explosion risk, poor financial trade-off, or increased safety/vessel cost.
- 2 Gives a second distinct valid reason from the official list.
Full-mark answer
1. The yield is already high at 86%, so the extra product would be limited. 2. Compressing the gases and using stronger, safer equipment would cost more and high pressure increases the risk of explosion.
Why this answer loses marks
A higher pressure is avoided because it would reduce the product yield.
Higher pressure would increase this yield; the valid objections concern limited benefit, energy, expense and safety.