AP Chemistry 7.10: Q and K Response

Practice AP Chemistry questions on comparing Q with K after a disturbance and predicting how concentrations or partial pressures redistribute to reach equilibrium.

Exam points

Explain how equilibrium composition depends on temperature, pressure and concentration in reversible reactions.
Apply equilibrium constants and reaction quotients to predict reaction shifts and system responses.

[Maximum number: 1]

Answer the following questions about magnesium.

The dissolution of magnesium hydroxide is represented by the following equation.

\mathrm{Mg}(\mathrm{OH})_{2}(s) \rightleftarrows \mathrm{Mg}^{2+}(a q)+2 \mathrm{OH}^{-}(a q) \quad K_{s p}=5.61 \times 10^{-12}

Using the reaction quotient, Q, predict whether a precipitate should form as the mixture

in beaker 3 approaches equilibrium. Justify your answer.

(iii) For the correct prediction and justification, consistent with part E (ii).

Examples of acceptable responses may include the following:

- $Q>K_{s p}$ , so a precipitate will form.

- The concentration of the ions in solution (represented by Q) is greater than that of a saturated solution, so a precipitate will form.

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7.10.A—Explain the relationships between Q, K, and the direction in which a reversible reaction will proceed to reach… question 1