AP Chemistry Unit 7.7: Equilibrium Concentrations

Practice AP Chemistry Unit 7.7 questions on predicting equilibrium concentrations from initial conditions and K, including reactions that proceed nearly to completion.

Exam points

Use thermodynamic and kinetic evidence to compare reaction direction, activation barriers, rates, and outcomes.
Interpret energy profiles and data to explain temperature, catalyst, and concentration effects on reactions.

Covered syllabus points

7.7.A—Identify the concentrations or partial pressures of chemical species at equilibrium based on the initial…

[Maximum number: 1]

A student investigates the reactions of nitrogen oxides. One of the reactions in the investigation requires an equimolar mixture of NO(g) and $\mathrm{NO}_{2}(g)$ , which the student produces by using the reaction represented above.

The student begins with an equimolar mixture of NO(g) and $\mathrm{NO}_{2}(g)$ in a rigid reaction vessel and the mixture reaches equilibrium at 298 K.

If both $P_{\mathrm{NO}}$ and $P_{\mathrm{NO}_{2}}$ in the vessel are initially 1.0 atm, will $P_{\mathrm{N}_{2} \mathrm{O}_{3}}$ at equilibrium be equal to 1.0 atm? Justify your answer.

No, the pressure will not equal 1.0 atm.

$P_{\mathrm{N}_{2} \mathrm{O}_{3}}$ would only equal 1.0 atm if the reaction goes to completion.

OR

The value of K indicates that a substantial amount of reactants will be present at equilibrium.

1 point is earned for a correct
choice and valid justification based on the value of K.

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Covered syllabus points

7.7 Calculating Equilibrium Concentrations question 1