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AP®ChemistryCollege BoardExam QuestionsUnit 7: EquilibriumEquilibrium Representation & Calculations

Equilibrium Representation & Calculations (College Board AP® Chemistry)

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Equilibrium Representation & Calculations

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Equilibrium Representation & Calculations

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11 mark

For the reaction

A2 (g) + B2 (g) ⇌ 2AB (g)

Diagram showing molecules. The key indicates open circles as A and filled circles as B, placed in a sealed container

What can be deduced about the value of Kp?

  • Kp almost equal to1

  • Kp < 1

  • Kp > 1

  • Using the data nothing can be concluded about the value of Kp.

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21 mark

For the reaction:

X2 (g) + Y2 (g) ⇌ 2XY (g)

The following represents the ratio of molecules at equilibrium at 25 °C in a 1.00 L sealed container. Assume that each particle in the diagram represents 1 mole.

Diagram with circles representing molecules: white circles for X, black circles for Y, paired in various combinations. A key explains the symbols.

Based on this information, what is the equilibrium constant, Kc, for the reaction above at 25°C?

  • 0.5

  • 12.5

  • 2

  • 0.08

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11 mark

2SO3 (g) ⇌  2SO2 (g)  + O2 (g)    Kc = 1.7 x 10-18 at 300 K

If the pressure of SO3 (g) was 0.060 M.

What is the concentration of O2 (g) at equilibrium?

  • 0.06 M

  • 6.12 x 10-21 M

  • 1.15 x 10-7 M

  • 6.12 x 10-21 M

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21 mark

PCl3 (g) + Cl2 (g) ⇌ PCl5 (g)

Kc = 50 at 450 oC

If the initial concentration of PCl3 was 0.30 M and Cl2 was 0.45 M, what is the concentration of PCl5 at equilibrium?

  • 1.30 M

  • 0.75 M

  • 1.68 M

  • 3.38 M

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31 mark

Br2 (g) + Cl2 (g) ⇌ 2BrCl (g)

Kp = 70 at 400 K

3.0 atm of Br2 (g) and Cl2 (g) are mixed in a sealed container at 400 K and left to reach equilibrium.

Which expression is the most appropriate to calculate the concentration of BrCl (g) at equilibrium?

  • 70 equals space fraction numerator 2 x over denominator 3.0 minus x end fraction

  • 70 equals space fraction numerator open parentheses 3.0 space minus space x close parentheses open parentheses 3.0 space minus x close parentheses over denominator 2 x squared end fraction

  • 70 equals space fraction numerator 2 x over denominator open parentheses 3.0 close parentheses open parentheses 3.0 close parentheses end fraction

  • 8.37 equals space fraction numerator 2 x over denominator open parentheses 3.0 minus x close parentheses end fraction

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