AP Chemistry : Properties of the Equilibrium Constant

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #136 : Reactions And Equilibrium

Calculate the equilibrium constant for \(\displaystyle 2 C(g) \Leftrightarrow A (g) + B (g)\) given the following information:

 

\(\displaystyle A (g) + B (g) \Leftrightarrow 2 C (g)\)      \(\displaystyle K_1 = 4.39 x 10^{-3}\)

\(\displaystyle 2 C(g) \Leftrightarrow D (g) + E (g)\)      \(\displaystyle K_2 = 1.15 x 10^4\)

Possible Answers:

\(\displaystyle 3.14 \, x \, 10^{-3}\)

\(\displaystyle 1.14\, x\, 10^2\)

\(\displaystyle 11.4\)

\(\displaystyle 22.8\)

\(\displaystyle 2.28 \, x \, 10^2\)

Correct answer:

\(\displaystyle 2.28 \, x \, 10^2\)

Explanation:

\(\displaystyle 2 C \Leftrightarrow A + B\)         \(\displaystyle K = 1/K_1= 228\)

Example Question #1 : Properties Of The Equilibrium Constant

Calculate the equilibrium constant for \(\displaystyle A (g) + B (g) \Leftrightarrow D (g) + E (g)\) given the following information:

 

\(\displaystyle A (g) + B (g) \Leftrightarrow 2 C (g)\)      \(\displaystyle K_1 = 4.39 \, x \, 10^{-3}\)

 

\(\displaystyle 2 C(g) \Leftrightarrow D (g) + E (g)\)      \(\displaystyle K_2 = 1.15 \, x \, 10^4\)

Possible Answers:

15.8

0.143

50.5

73.2

25.3

Correct answer:

50.5

Explanation:

\(\displaystyle A + B \Leftrightarrow 2 C\)      \(\displaystyle K_1 = 4.39 x 10^{-3}\)

\(\displaystyle 2C \Leftrightarrow D + E\)      \(\displaystyle K_2 = 1.15 x 10^{-4}\)

\(\displaystyle K = K_1 K_2 = (4.39 x 10^{-3}) (1.15 x 10^{-4}) = 50.5\)

Example Question #1 : Properties Of The Equilibrium Constant

Calculate the equilibrium constant for \(\displaystyle N_2 (g) + O_2 (g) + Cl_2 (g) \Leftrightarrow 2 \: NOCl\)given the following information:

 

\(\displaystyle \frac{1}{2}N_2 + O_2(g) \Leftrightarrow NO_2 (g)\)                    \(\displaystyle K_1 = 1.0 \, x \, 10^{-9}\)

 

\(\displaystyle NOCl(g) + \frac{1}{2} O_2 (g) \Leftrightarrow NO_2Cl\)        \(\displaystyle K_2 = 1.1 \, x\, 10^2\)

\(\displaystyle NO_2 (g) + \frac{1}{2} Cl_2 \Leftrightarrow NO_2Cl\)                \(\displaystyle K_3 = 0.3\)

Possible Answers:

\(\displaystyle 7\, x\, 10^{-24}\)

\(\displaystyle 5 \, x \, 10^{-10}\)

\(\displaystyle 7\, x\, 10^{-8}\)

\(\displaystyle 3\, x\, 10^{-3}\)

\(\displaystyle 11\)

Correct answer:

\(\displaystyle 7\, x\, 10^{-24}\)

Explanation:

\(\displaystyle 2 (1/2 N_2 + O_2 \Leftrightarrow 2 NO_2 )\)                         \(\displaystyle K = K_1^2 = 1 x 10^{-18}\)

\(\displaystyle 2 (NO_2Cl \Leftrightarrow NOCl + 1/2 O_2)\)               \(\displaystyle K = (1/K_2)^2 = 8.3 x 10^{-5}\)

\(\displaystyle 2 (NO_2 + 1/2 Cl_2 \Leftrightarrow NO_2Cl)\)                  \(\displaystyle K = K_3^2 = 0.09\)

 

\(\displaystyle K = (1 x 10^{-18}) (8.3 x 10^{-5}) (0.09) = 7 x 10^{-24}\)

Example Question #141 : Reactions And Equilibrium

Calculate the equilibrium constant for \(\displaystyle 2 NH_3 (g) + 3 I_2 (g) \Leftrightarrow N_2 (g) + 6 HI (g)\) given the following information:

 

\(\displaystyle N_2 (g) + 3 H_2 (g) \Leftrightarrow 2 NH_3(g)\)             \(\displaystyle K_1 = 0.50\)

 

\(\displaystyle H_2 (g) + I_2 (g) \Leftrightarrow 2 HI (g)\)                    \(\displaystyle K_2 = 50\)

Possible Answers:

\(\displaystyle 3.2 x 10^{-3}\)

\(\displaystyle 2.8 x 10^6\)

\(\displaystyle 5.6 x 10^4\)

\(\displaystyle 1.5 x 10^3\)

\(\displaystyle 2.5 x 10^5\)

Correct answer:

\(\displaystyle 2.5 x 10^5\)

Explanation:

\(\displaystyle 2 NH_3 \Leftrightarrow N_2 + 3 H_2\)           \(\displaystyle K = 1/K_1 = 2\)

\(\displaystyle 3 ( H_2 + I_2 \Leftrightarrow 2 HI)\)            \(\displaystyle K = K_2^3 = 1.25 x 10^5\)

 

\(\displaystyle K = (2) (1.25 x 10^5) = 2.5 x 10^5\)

Example Question #3 : Properties Of The Equilibrium Constant

Calculate the equilibrium constant for \(\displaystyle 2 HI (g) \Leftrightarrow H_2 (g) + I_2 (g)\) given the following information:

 

\(\displaystyle H_2(g) + I_2 (g) \Leftrightarrow 2 HI (g)\)               \(\displaystyle K_1 = 50\)

Possible Answers:

\(\displaystyle 0.05\)

\(\displaystyle 0.02\)

\(\displaystyle 0.01\)

\(\displaystyle 1.21\)

\(\displaystyle 0.25\)

Correct answer:

\(\displaystyle 0.02\)

Explanation:

\(\displaystyle 2 HI \Leftrightarrow H_2 + I_2\)               \(\displaystyle K = 1/K_1 = 0.02\)

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