For the equilibrium N2 + 3H2 gives 2NH3, which is exothermic, the yield of ammonia is increased by
Correct answer: B. raising the pressure and lowering the temperature
- A. raising the temperature and lowering the pressure
- B. raising the pressure and lowering the temperature
- C. adding a catalyst
- D. removing nitrogen from the mixture
Explanation
There are four moles of gas on the left and two on the right, so high pressure pushes the equilibrium towards the smaller volume, and since the forward reaction releases heat a lower temperature also favours it. A catalyst speeds the approach to equilibrium without changing the yield at all, which is the standard trap. In practice a compromise temperature near 450 degrees Celsius is used because the reaction is too slow when cold.
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About Le Chatelier's Principle
Le Chatelier's principle predicts how an equilibrium responds when concentration, pressure or temperature changes. Questions apply it to reversible reactions, identify the direction of shift and distinguish genuine equilibrium changes from the effect of a catalyst, which changes the rate of reaching equilibrium but not its position.
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