Worksheet: Equilibrium Constants and Concentrations

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In this worksheet, we will practice converting between equilibrium constant expressions and the concentrations of reactants and products.

Q1:

Consider the equilibrium of the HPO42– ion acting as a weak base. HPO()+HO()HPO()+OH()42–224––aqlaqaq What is the equilibrium constant for this reaction under these conditions?

  • [OH]– = 1.3×10 M,
  • [HPO]24– = 0.042 M,
  • [HPO]42– = 0.341 M.
  • A1.6×10
  • B4.4×10
  • C5.5×10
  • D6.7×10
  • E1.1×10

Q2:

Consider the shown equilibrium. N()+3H()2NH()atC223cggg,𝐾=0.50400.∘

Analysis of the gases in a sealed reaction vessel containing NH3, N2, and H2 at equilibrium at 400∘C established the concentration of N2 to be 1.2 M and the concentration of H2 to be 0.24 M. What is the equilibrium molar concentration of NH3?

  • A0.14 M
  • B0.38 M
  • C8.3×10 M
  • D10 M
  • E9.1×10 M

Q3:

Cobalt metal can be prepared by reducing cobalt(II) oxide with carbon monoxide, as shown in the equation.CoO()+CO()Co()+CO(),atCsgsg2c𝐾=4.90×10550∘ What concentration of CO remains in an equilibrium mixture with [CO]2 = 0.100 M?

  • A4.90×10 M
  • B2.04×10 M
  • C10.0×10 M
  • D4.90×10 M
  • E2.40×10 M

Q4:

Carbon is reacted with water vapor at 1,000∘C, establishing the shown equilibrium. C()+HO()CO()+H(),atCsggg22c𝐾=0.2001,000.∘ What is the concentration of CO in the equilibrium mixture if [HO]2 = 0.750 M?

Q5:

Consider the shown equilibrium. NO“(chloroform)”2NO“(chloroform)”242c,𝐾=1.07×10.

What is the equilibrium concentration of NO2 in 1.00 L of a solution prepared from 0.129 mol of NO24 with chloroform as the solvent? Assume that the change in concentration of NO24 is small enough to be neglected.

  • A1.17×10 M
  • B1.38×10 M
  • C8.29×10 M
  • D5.87×10 M
  • E6.90×10 M

Q6:

Pure PCl5 decomposes reversibly into PCl3 and Cl2, as shown. PCl()PCl()+Cl()532cggg,𝐾=0.0211 The initial concentration of PCl5 is 2.00 M. Calculate the equilibrium concentration of Cl2.

Q7:

What is the concentration of NO in an equilibrium mixture at 250∘C that results from the reaction of 0.20 M   NO and 0.10 M  O2, as shown? 2NO()+O()2NO()atCggg22c,𝐾=2.3×10250.∘

  • A0.0070 M
  • B0.0044 M
  • C0.012 M
  • D0.0035 M
  • E0.0056 M

Q8:

Consider the shown equilibrium. H+I2HIatC22c,𝐾=50.2448∘

How many grams of HI are present in an equilibrium mixture containing 1.25 mol of H2 and 63.5 g of I2 at 448∘C?

Q9:

Consider the shown equilibrium. CaCO()CaO()+CO()32ssg

What is the minimum mass of CaCO3 required to establish equilibrium at a certain temperature in a 6.50 L container if the equilibrium constant (𝐾c) is 0.050 for the decomposition reaction of CaCO3 at that temperature?

Q10:

Carbon monoxide and water react at high temperature according to the shown equation. CO()+HO()CO()+H()gggg222 Under certain conditions, the equilibrium constant for this reaction (𝐾c) is 5.0.

An equilibrium mixture of the substances was found to contain 0.20 mol of CO, 0.30 mol of water vapor, and 0.90 mol of H2 per liter of gas. How many moles of CO2 were present in the equilibrium mixture?

Additional H2 was added to the system at the same temperature, and some water vapor was removed by drying. A new equilibrium mixture was thereby established containing 0.40 mol of CO, 0.30 mol of water vapor, and 1.2 mol of H2 per liter of gas. How many moles of CO2 were there in the new equilibrium mixture?

Q11:

Antimony pentachloride decomposes according to the following equation. SbCl()SbCl()+Cl()532ggg An equilibrium mixture in a 5.00 L flask at 448∘C contains 3.85 g of SbCl5, 9.14 g of SbCl3, and 2.84 g of Cl2. How many grams of antimony pentachloride would be present if this mixture were transferred into a 2.00 L flask at the same temperature?

Q12:

Sucrose is hydrolyzed to fructose and glucose according to the equation. CHO()+HO()CHO()+CHO()rate[CHO]122211261266126122211aqlaqaq,=𝑘

This reaction follows a first-order rate law. The products are structural isomers, exhibiting the same structural formula CHO6126.

In neutral solution, 𝑘 = 2.1×10 s−1 at 27∘C. In the human body, the rate of this reaction is catalyzed by an enzyme, increasing the rate constant to 1.36×10 at 27∘C. What is the concentration of fructose after a 0.150 M aqueous solution of sucrose has reached equilibrium?

Q13:

Gaseous nitrogen dioxide forms dinitrogen tetroxide according to the following equation. 2NO()NO()224gg When 0.10 mol  NO2 is added to a 1.0 L flask at 25∘C, the concentration changes so that, at equilibrium, [NO]=0.016M2 and [NO]=0.042M24.

What is the value of the reaction quotient before any reaction occurs?

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

  • A0.38
  • B2.6
  • C6.1×10
  • D1.6×10
  • E4.2

Q14:

Consider the shown reaction. 2SO()+O()2SO()223ggg For this reaction, the concentrations at equilibrium are [SO]2 = 0.90 M, [O]2 = 0.35 M, and [SO]3 = 1.1 M. What is the value of the equilibrium constant, 𝐾c?

Q15:

Iodine molecules react reversibly with iodide ions to produce triiodide ions, as shown.I()+I()I()2–3–aqaqaq Before a reaction, the concentrations of I2 and I– in a solution are both equal to 1.000×10 M. At equilibrium, the concentration of I2 is 6.61×10 M. If the concentrations of all species are 1.000 M under standard conditions, calculate the equilibrium constant for this reaction.

Q16:

Ethanol and acetic acid react to form water and ethyl acetate, the solvent responsible for the odor of some nail polish removers, as shown. CHOH+CHCOHCHCOCH+HO253232252 When 1.00 mol of each of CHOH25 and CHCOH32 are allowed to react in 1.00 L of the solvent dioxane, equilibrium is established when 13 mol of each of the reactants remains. What is the equilibrium constant, 𝐾c, for the reaction?

Q17:

The equilibrium constant for the reaction of nitrogen and hydrogen to produce ammonia at a certain temperature is 6.00×10. What is the equilibrium concentration of ammonia if the equilibrium concentrations of nitrogen and hydrogen are 4.26 M and 2.09 M respectively?

Q18:

Under certain conditions, the equilibrium constant 𝐾c for the decomposition of PCl()5g into PCl()3g and Cl()2g is 0.0211. What is the equilibrium concentration of PCl5 if its initial concentration is 1.00 M?

Q19:

Acetic acid, CHCOH32, reacts with ethanol, CHOH25, to form water and ethyl acetate, CHCOCH3225, as shown. CHCOH+CHOHCHCOCH+HO322532252 The equilibrium constant for this reaction in dioxane is 4.0. A dioxane solution contains 0.15 M acetic acid, 0.15 M ethanol, 0.40 M ethyl acetate, and 0.40 M water when initially prepared. Calculate the concentration of ethyl acetate at equilibrium.

Q20:

Consider the shown equilibrium. H()+I()2HI()22ggg

A 1.00 L flask is filled with 1.00 mole of H2 and 2.00 moles of I2. The value of the equilibrium constant for the reaction of hydrogen and iodine reacting to form hydrogen iodide is 50.5 under the given conditions. Calculate the equilibrium concentration of HI in the 1.00 L flask.

Q21:

Consider the shown equilibrium. HCN()H()+CN()aqaqaq+–c,𝐾=4.9×10

What is the approximate concentration of H+ at equilibrium for a 0.15 M solution of HCN?

  • A8.6×10 M
  • B1.5×10 M
  • C4.9×10 M
  • D3.3×10 M
  • E2.1×10 M

Q22:

Consider the shown equilibrium. NH()+HO()NH()+OH()324+–caqlaqaq,𝐾=1.8×10

What is the equilibrium concentration of NH4+ in a 0.25 M aqueous solution of NH3?

  • A1.8×10 M
  • B3.6×10 M
  • C9.1×10 M
  • D2.1×10 M
  • E4.5×10 M

Q23:

Copper(II) ions form a complex ion in the presence of ammonia, as shown. Cu()+4NH()Cu(NH)()2+3342+caqaqaq,𝐾=5.0×10. If 0.010 mol  Cu2+ is added to 1.00 L of a 1.00 M  NH3 solution, what is the concentration of Cu2+ when the system comes to equilibrium?

  • A2.1×10 M
  • B1.1×10 M
  • C7.0×10 M
  • D6.7×10 M
  • E2.4×10 M

Q24:

Consider the shown equilibrium. Ni()+6NH()Ni(NH)()2+3362+caqaqaq,𝐾=5.5×10

What is the approximate equilibrium concentration of Ni2+ when 0.25 mol  Ni2+ is added to 1.00 L of a 2.00 M  NH3 solution?

  • A1.9×10 M
  • B1.7×10 M
  • C2.9×10 M
  • D1.7×10 M
  • E5.5×10 M

Q25:

The equilibrium constant, 𝐾, of a process may change if it is calculated relative to different standard conditions. For which process does the choice of standard conditions have no effect on 𝐾?

  • ACl()2Cl()2gg
  • BBr()+Cl()2BrCl()22ggg
  • CHCO()HO()+CO()2322aqlaq
  • DH()+Cl()HCl()+–aqaqaq
  • ECaCO()CaO()+CO()32ssg

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