AP Chemistry 7.4: Equilibrium Constant Calculations

Practice AP Chemistry questions on calculating equilibrium constants from experimental concentrations or partial pressures using stoichiometric changes and equilibrium data.

Exam points

Explain how thermodynamic quantities such as enthalpy, entropy and Gibbs energy describe chemical change.
Apply thermodynamic relationships to predict spontaneity, equilibrium and energy transfer in reactions.

[Maximum number: 1]

In the gas phase, $\mathrm{AlCl}_{3}$ is a molecular substance. A reaction of gaseous $\mathrm{AlCl}_{3}$ at high temperature is represented by the following balanced equation.

\text { Reaction 1: } \mathrm{AlCl}_{3}(g) \rightarrow \mathrm{Al}(g)+3 \mathrm{Cl}(g) \quad \Delta H_{1}^{\circ}=\text { ? }

Using the particle-level diagram, calculate the value of $K_{p}$ for the reaction if the total pressure in the container is 22.1 atm.

For the correct calculated value, consistent with part (e): 1 point

K_{p}=\frac{\chi_{\mathrm{Al}_{2} \mathrm{Cl}_{6}}\left(P_{\text {total }}\right)}{\left(\chi_{\mathrm{AlCl}_{3}}\left(P_{\text {total }}\right)\right)^{2}}=\frac{\frac{3}{10}(22.1)}{\left(\frac{7}{10}(22.1)\right)^{2}}=0.0277

Total for question 210 points

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7.4.A—Calculate Kc or Kp based on experimental observations of concentrations or pressures at equilibrium question 1