IB Chemistry HL 2.3.2 Equilibrium Law Questions

Use real HL exam questions to write and apply Kc expressions from balanced homogeneous equilibrium equations, including scaled reactions.

Exam points

Write Kc from the balanced equation using product and reactant concentrations raised to their stoichiometric powers.
Calculate or transform Kc by substituting equilibrium concentrations or reversing/scaling the balanced equation while keeping stoichiometric exponents aligned.

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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}

Deduce the equilibrium constant expression, $K_{\mathrm{c}}$ , for the reaction on page 10.

$\left(K_{\mathrm{c}}=\right) \frac{\left[\mathrm{NH}_{3}(\mathrm{~g})\right]^{2}}{\left[\mathrm{N}_{2}(\mathrm{~g})\right] \times\left[\mathrm{H}_{2}(\mathrm{~g})\right]^{3}}$ ;

Ignore state symbols.
Concentrations must be represented by square brackets.

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IB Chemistry HL 2.3.2 Equilibrium Law Questions question 1