Use real HL exam questions to predict equilibrium shifts and Kc/composition changes after concentration, temperature and pressure changes.
When nitrogen gas and hydrogen gas are allowed to react in a closed container the following equilibrium is established.
Predict, with a reason, how each of the following changes affects the position of equilibrium.
The volume of the container is increased.
Ammonia is removed from the equilibrium mixture.
The volume of the container is increased: position of equilibrium shifts to the left/reactants and fewer moles of gas on the right hand side/pressure decreases / OWTTE;
Ammonia is removed from the equilibrium mixture: position of equilibrium shifts to the right/products and [ NH3 ] decreases so [ N2 ] and [ H2 ] must also decrease to keep Kc constant OR
position of equilibrium shifts to the right/products and rate of reverse reaction decreases / OWTTE;
Award [1 max] if both predicted changes are correct.
Do not accept "to increase [ NH3 ]" or reference to LCP without explanation.
Typical conditions used in the Haber process are 500∘C and 200 atm , resulting in approximately 15 % yield of ammonia.
Outline why a pressure higher than 200 atm is not often used.
high cost for building/maintaining plant/ high energy cost of compressor / OWTTE;
Do not accept "high pressure is expensive" without justification.
Accept high pressure requires high energy.