IB Chemistry HL 2.3.6 Hl Equilibrium Calculations Questions

Use real HL exam questions to build stoichiometric equilibrium tables and calculate K or unknown equilibrium concentrations from measured data.

Exam points

Build initial, change and equilibrium quantities from the balanced equation, converting moles and volumes to consistent equilibrium concentrations.
Substitute equilibrium data into the balanced equilibrium expression to calculate K or an unknown equilibrium concentration while preserving stoichiometric powers.

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Study 2.3.6 (HL)—Equilibrium calculations conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[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 $K_{\mathrm{c}}=14.86$ .

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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IB Chemistry HL 2.3.6 Hl Equilibrium Calculations Questions question 1