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AP®ChemistryCollege BoardExam QuestionsUnit 7: EquilibriumEquilibrium Constants

Equilibrium Constants (College Board AP® Chemistry)

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Equilibrium Constants

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Equilibrium Constants

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11 mark

2NOCl (g)   ⇌   2NO +  Cl2 (g)

Nitrosyl chloride decomposes into nitrogen monoxide and chlorine according to the equation above.

What is the correct formulation of the equilibrium expression of the reaction?

  • fraction numerator left square bracket NOCl right square bracket squared over denominator left square bracket NO right square bracket squared space left square bracket Cl subscript 2 right square bracket end fraction

  • fraction numerator left square bracket NO right square bracket space left square bracket Cl subscript 2 right square bracket over denominator left square bracket NOCl right square bracket end fraction

  • fraction numerator 2 left square bracket NO right square bracket space left square bracket Cl subscript 2 right square bracket over denominator 2 left square bracket NOCl right square bracket end fraction

  • fraction numerator left square bracket NO right square bracket squared space left square bracket Cl subscript 2 right square bracket over denominator left square bracket NOCl right square bracket squared end fraction

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21 mark

The reaction

N2 (g) + 3H2 (g)  rightwards harpoon over leftwards harpoon  2NH3 (g)

has an equilibrium constant value of 2.7 x 103 at a certain temperature

What is the equilibrium constant of

 4NH3 (g )  rightwards harpoon over leftwards harpoon 2N2 (g) + 6H2 (g)?

  • 7.3 x 106

  • 2.7 x 103

  • 1.37 x 10-7

  • 1.37 x 10-4

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31 mark

3O2 (g) ⇌ 2O3 (g) 

What is the value of the equilibrium constant when the equilibrium concentrations are [O2] = 0.8 M and [O3] = 0.8 M ?

  • 1.25

  • 1

  • 0.64

  • 0.8

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41 mark

 A (g) + 2B (g) ⇌  X (g) + Y (g) 

The reaction above has a value of Kp = 1.0 x 10-4 at 25 degreeC.

Which of the following relationships is correct about this equilibrium at 25 degreeC?

  • The partial pressure of A will be equal to the partial pressure of Y

  • The partial pressure of A will be greater than the partial pressure of X

  • The partial pressure of A will be less than the partial pressure of Y

  • The partial pressure of B will be equal to the partial pressure of Y

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51 mark

2N2O5 (g)  ⇌ 4NO2 (g) + O2 (g)

When gaseous dinitrogen pentoxide, N2O5 (g), decomposes at 358 K, the equilibrium above is established.

2.0 mol of N2O5 (g) were placed in a 1.0 dm3 container and allowed to reach equilibrium. At equilibrium 1.0 mol of N2O5 (g) were present.

What is the value of Kc?

  • 0.125

  • 1

  • 2

  • 8

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61 mark

The reaction between nitrogen and hydrogen produces ammonia gas:

N2 (g) + 3H2 (g)  rightwards harpoon over leftwards harpoon  2NH3 (g)

If the equilibrium constant for the reaction is x, what is the equilibrium constant for the following reaction?

2N2 (g) + 6H2 (g)  rightwards harpoon over leftwards harpoon  4NH3 (g)

  • x

  • 2x

  • x2

  • 2x2

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11 mark

The equilibrium reaction below has an equilibrium constant K=1.1

2X⇋Y

Based on the value of K, which of the following must be true?

  • [X] ≫ [Y]

  • [X] ＞[Y]

  • [X] = [Y]

  • [X] ＜ [Y]

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21 mark

Consider the following reaction at different temperatures. The equilibrium constant (K) values were measured at each temperature:

Temperature

Kc value

T1

1 x 10-2

T2

1 x 101

T3

1

T4

1 x 102

Which of the following correctly ranks the amount of products in the equilibrium mixtures from least to most?

  • T1 ＜T2 ＜T3＜T4

  • T4 ＜T3 ＜T2＜T1

  • T4 ＜T2 ＜T3＜T1

  • T1 ＜T3 ＜T2＜T4

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31 mark

Consider the following two equilibrium reactions:

2NOBr (g) ⇋ 2NO (g) + Br2 (g), with equilibrium constant Kc1

NO (g) + 1 halfBr2 (g) ⇋ NOBr (g), with equilibrium constant Kc2

Which of the following is the correct mathematical relationship between Kc1 and Kc2​?

  • 2Kc2 = Kc1

  • (Kc2)2 = Kc1

  • Kc2 = fraction numerator 1 over denominator square root of K subscript straight c 1 end subscript end root end fraction

  • Kc2 = fraction numerator 1 over denominator 2 K subscript c 1 end subscript end fraction

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41 mark

Consider the following equilibrium reaction:

2NO (g) + 2H2 (g) rightwards harpoon over leftwards harpoon N2 (g) + 2H2O (g)

Initially, the following concentrations were present in a 1.0 dm3 flask:

  • [NO] = 0.20 mol / dm3

  • [H2]=0.08 mol / dm3

  • [H2O]=0.10 mol / dm3

At equilibrium, the concentration of H2​ is found to be 0.02 mol/dm3.

What is the value of the equilibrium constant for this reaction?

  • 1.02 x 10-2

  • 98.0

  • 8.3

  • 489.8

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