IB Chemistry HL 2.3.6 Equilibrium calculations Question Bank

Practise IB Chemistry HL 2.3.6 by applying equilibrium calculations to exam-style questions.

Exam points

identify the relevant chemical structure, process or evidence
apply the correct chemical model or equation
evaluate the result using chemical reasoning and data

[Maximum number: 2]

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}

When 1.00 mol of nitrogen and 3.00 mol of hydrogen were allowed to reach equilibrium in a $1.00 \mathrm{dm}^{3}$ container at a temperature of $500^{\circ} \mathrm{C}$ and a pressure of 1000 atm , the equilibrium mixture contained 1.46 mol of ammonia.

Calculate the value of $K_{\mathrm{c}}$ at $500^{\circ} \mathrm{C}$ .

moles at equilibrium: nitrogen 0.27 , hydrogen 0.81 / concentrations at equilibrium: nitrogen $0.27\left(\mathrm{~mol} \mathrm{dm}^{-3}\right)$ , hydrogen $0.81\left(\mathrm{~mol} \mathrm{dm}^{-3}\right)$ (and ammonia $1.46 \mathrm{~mol} \mathrm{dm}^{-3}$ );
$K_{\mathrm{c}}=15$ ;

Actual calculation gives $K_{c}=14.86$ .

Marking guidance:

Award [2] for correct final answer.
Award [1 max] if $K_{\mathrm{c}}\left(=\frac{1.46^{2}}{3^{3} \times 1}\right)=0.079$

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2.3.6 (HL)—Equilibrium calculations question 1