IB Chemistry HL 2.3.4 Le Châtelier's principle Question Bank

Practise IB Chemistry HL 2.3.4 by applying le châtelier's principle to exam-style questions.

[Maximum number: 3]

When nitrogen gas and hydrogen gas are allowed to react in a closed container the following equilibrium is established.

\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g}) \quad \Delta H=-92.6 \mathrm{~kJ}

(a)

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.

[ 2 ]

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 [ $\mathrm{NH}_{3}$ ] decreases so [ $\mathrm{N}_{2}$ ] and [ $\mathrm{H}_{2}$ ] must also decrease to keep $K_{\mathrm{c}}$ constant OR
position of equilibrium shifts to the right/products and rate of reverse reaction decreases / OWTTE;

Marking guidance:

Award [1 max] if both predicted changes are correct.
Do not accept "to increase [ $\mathrm{NH}_{3}$ ]" or reference to LCP without explanation.

(b)

Typical conditions used in the Haber process are $500^{\circ} \mathrm{C}$ and 200 atm , resulting in approximately 15 % yield of ammonia.

[ 1 ]

(i)

Outline why a pressure higher than 200 atm is not often used.

[ 1 ]

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2.3.4—Le Châtelier's principle question 1

Question (a)

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Question (i)