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16. Chemical Equilibrium

Equilibrium Constant Calculations

16. Chemical Equilibrium

Equilibrium Constant Calculations

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Equilibrium Constant Calculations

Equilibrium Constant Calculations

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Multiple Choice

The reaction: 2 NO(g) + Br₂(g) ⇌ 2 NOBr(g), has a K_p of 2.5 x 10² at 35°C. Calculate the equilibrium concentration of NOBr, if equilibrium concentrations of NO and Br₂ are 0.2 atm and 0.050 atm, respectively.

Multiple Choice

For the reaction below, K_c = 1.5 at a constant temperature. A 3.2 L flask contains an equilibrium mixture of 3 compounds: 3.7 g of NH₄HS, 70. g of NH₃ and unknown amount of H₂S. What is the mass (grams) of H₂S produced at equilibrium?

NH₄HS(s) ⇌ NH₃(g) + H₂S(g)

Textbook Question

The diagram shown here represents the equilibrium state for the reaction A21g2 + 2 B1g2 Δ 2 AB1g2. (a) Assuming the volume is 2 L, calculate the equilibrium constant Kc for the reaction. [Sections 15.5 and 15.7]

Textbook Question

The following equilibria were attained at 823 K:

CoO(s) + H₂(g) → Co(s) + H₂O(g) K_c = 67

CoO(s) + CO(g) → Co(s) + CO₂(g) K_c = 490

Based on these equilibria, calculate the equilibrium constant for H₂(g) + CO₂(g) → CO(g) + H₂O(g) at 823 K.

Textbook Question

Calculate the value of the equilibrium constant at 427 °C for the reaction

Na O1s2 + 1>2 O 1g2 ∆ Na O 1s2

given the following equilibrium constants at 427 °C.

Na2O1s2 ∆ 2 Na1l2 + 1>2 O21g2 Kc = 2 * 10-25 Na O 1s2 ∆ 2 Na1l2 + O 1g2 K = 5 * 10-29

Textbook Question

Ethene (C2H4) can be halogenated by this reaction: C2H4(g) + X2(g) ⇌ C2H4X2(g) where X2 can be Cl2 (green), Br2 (brown), or I2 (purple). Examine the three figures representing equilibrium concentrations in this reaction at the same temperature for the three different hal- ogens. Rank the equilibrium constants for the three reactions from largest to smallest.

Textbook Question

The equilibrium 2 NO1g2 + Cl21g2 Δ 2 NOCl1g2 is established at 500 K. An equilibrium mixture of the three gases has partial pressures of 0.095 atm, 0.171 atm, and 0.28 atm for NO, Cl2, and NOCl, respectively. (a) Calculate Kp for this reaction at 500.0 K.

Textbook Question

Phosphorus trichloride gas and chlorine gas react to form phosphorus pentachloride gas: PCl31g2 + Cl21g2 Δ PCl51g2. A 7.5-L gas vessel is charged with a mixture of PCl31g2 and Cl21g2, which is allowed to equilibrate at 450 K. At equilibrium the partial pressures of the three gases are PPCl3 = 0.124 atm, PCl2 = 0.157 atm, and PPCl5 = 1.30 atm. (a) What is the value of Kp at this temperature?

Textbook Question

Consider the reaction: N (g) + 3H (g) ⇌ 2NH (g) Complete the table. Assume that all concentrations are equilib- rium concentrations in M. T (K) [n2] [H2] [nH3] Kc 500 0.115 0.105 0.439 575 0.110 ________ 0.128 775 0.120 0.140 ________ ________ 9.6 0.0584

Textbook Question

Consider the following reaction: H2(g) + I2(g) ⇌ 2 HI(g) Complete the table. Assume that all concentrations are equilib- rium concentrations in M. T (°C) [H2] [i2] [Hi] Kc 25 0.0355 0.0388 340 ________ 0.0455 445 0.0485 0.0468 0.922 ________ 0.387 9.6 ________ 50.2

Textbook Question

Consider the reaction: 2NO(g) + Br2(g) ⇌ 2NOBr(g) Kp = 28.4 at 298K In a reaction mixture at equilibrium, the partial pressure of NO is 108 torr and that of Br2 is 126 torr. What is the partial pressure of NOBr in this mixture?

Textbook Question

Consider the reaction: SO2Cl2(g) ⇌ SO2(g) + Cl2(g) Kp = 2.91*10^3 at 298 K In a reaction at equilibrium, the partial pressure of SO2 is 137 torr and that of Cl2 is 285 torr. What is the partial pressure of SO2Cl2 in this mixture?

Textbook Question

Consider the interconversion of A molecules (red spheres) and B molecules (blue spheres) according to the reaction A ∆ B. Each of the series of pictures at the right represents a separate experiment in which time increases from left to right: (b) What is the value of the equilibrium constant Kc for the reaction A ∆ B?

Textbook Question

At 900 K, the following reaction has Kp = 0.345: 2 SO21g2 + O21g2 Δ 2 SO31g2 In an equilibrium mixture the partial pressures of SO2 and O2 are 0.135 atm and 0.455 atm, respectively. What is the equilibrium partial pressure of SO3 in the mixture?

Textbook Question

The following picture represents the equilibrium state for the reaction 2 AB ∆ A2 + B2. Which rate constant is larger, kf or kr? Explain.

Textbook Question

At 373 K, Kp = 0.416 for the equilibrium 2 NOBr1g2 Δ 2 NO1g2 + Br21g2 If the pressures of NOBr(g) and NO(g) are equal, what is the equilibrium pressure of Br21g2?

Textbook Question

At 218 C, Kc = 1.2 * 10-4 for the equilibrium NH4SH1s2 Δ NH31g2 + H2S1g2 Calculate the equilibrium concentrations of NH3 and H2S if a sample of solid NH4SH is placed in a closed vessel at 218 C and decomposes until equilibrium is reached.

Textbook Question

At 80 C, Kc = 1.87 * 10-3 for the reaction PH3BCl31s2 Δ PH31g2 + BCl31g2 (b) If the flask has a volume of 0.250 L, what is the minimum mass of PH3BCl31s2 that must be added to the flask to achieve equilibrium?

Textbook Question

At 80 C, Kc = 1.87 * 10-3 for the reaction PH3BCl31s2 Δ PH31g2 + BCl31g2 (a) Calculate the equilibrium concentrations of PH3 and BCl3 if a solid sample of PH3BCl3 is placed in a closed vessel at 80 C and decomposes until equilibrium is reached.

Textbook Question

At 25 C, the reaction CaCrO41s2ΔCa2+1aq2 + CrO4 2-1aq2 has an equilibrium constant Kc = 7.1 * 10-4. What are the equilibrium concentrations of Ca2 + and CrO4 2- in a saturated solution of CaCrO4?

Textbook Question

The value of Kc for the reaction 3 O21g2 ∆ 2 O31g2 is 1.7 * 10-56 at 25°C. Do you expect pure air at 25 °C to contain much O3 (ozone) when O2 and O3 are in equilib- rium? If the equilibrium concentration of O2 in air at 25 °C is 8 * 10-3 M, what is the equilibrium concentration of O3?

Textbook Question

An equilibrium mixture of N2, H2, and NH3 at 700 K con- tains 0.036 M N2 and 0.15 M H2. At this temperature, Kc for the reaction N21g2 + 3 H21g2 ∆ 2 NH31g2 is 0.29. What is the concentration of NH3?

Textbook Question

The value of Kc for the reaction of acetic acid with ethanol is 3.4 at 25°C: CH3CO2H1soln2 + CH3CH2OH1soln2 ∆ Acetic acid Ethanol CH3CO2CH2CH31soln2 + H2O1soln2 Kc = 3.4 (a) How many moles of ethyl acetate are present in an equi- librium mixture that contains 4.0 mol of acetic acid, 6.0 mol of ethanol, and 12.0 mol of water at 25 °C?

Textbook Question

In Section 11.5, we defined the vapor pressure of a liquid in terms of an equilibrium. (c) What is the value of Kp for any liquid in equilibrium with its vapor at the normal boiling point of the liquid?

Textbook Question

Consider the reaction of chloromethane with OH- in aque- ous solution: CH Cl1aq2 + OH-1aq2 ∆kf CH OH1aq2 + Cl-1aq2 At 25 °C, the rate constant for the forward reaction is 6 * 10-6 M-1 s-1, and the equilibrium constant Kc is 1 * 1016. Calculate the rate constant for the reverse reac- tion at 25 °C.

Textbook Question

Consider the sublimation of mothballs at 27 °C in a room having dimensions 8.0 ft * 10.0 ft * 8.0 ft. Assume that the mothballs are pure solid naphthalene 1density 1.16 g>cm32 and that they are spheres with a diameter of 12.0 mm. The equilibrium constant Kc for the sublimation of naphthalene is 5.40 * 10-6 at 27 °C. C10H81s2 ∆ C10H81g2 (b) How many mothballs are required to saturate the room with gaseous naphthalene?

Textbook Question

Consider the sublimation of mothballs at 27 °C in a room having dimensions 8.0 ft * 10.0 ft * 8.0 ft. Assume that the mothballs are pure solid naphthalene 1density 1.16 g>cm32 and that they are spheres with a diameter of 12.0 mm. The equilibrium constant Kc for the sublimation of naphthalene is 5.40 * 10-6 at 27 °C. C10H81s2 ∆ C10H81g2 (a) When excess mothballs are present, how many gaseous naphthalene molecules are in the room at equilibrium?

Textbook Question

Ozone is unstable with respect to decomposition to ordi-nary oxygen: 2 O31g2 ∆ 3 O21g2 Kp = 1.3 * 1057 How many O3 molecules are present at equilibrium in 10 mil-lion cubic meters of air at 25 °C and 720 mm Hg pressure?

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