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 H P O 4 2 – ion acting as a weak base: A solution containing a mixture of N a H P O 2 4 and N a H P O 2 4 at equilibrium has the following concentrations:

  • [ O H ] – = 1 . 3 × 1 0 − 6 M,
  • [ H P O ] 2 4 – = 0.042 M,
  • [ H P O ] 4 2 – = 0.341 M.

What is the equilibrium constant for this reaction under these conditions?

  • A 4 . 4 × 1 0 − 7
  • B 5 . 5 × 1 0 − 8
  • C 1 . 1 × 1 0 − 5
  • D 1 . 6 × 1 0 − 7

Q2:

Consider the equilibrium

Analysis of the gases in a sealed reaction vessel containing N H 3 , N 2 , and H 2 at equilibrium at 4 0 0 ∘ C established the concentration of N 2 to be 1.2 M and the concentration of H 2 to be 0.24 M. What is the equilibrium molar concentration of N H 3 ?

  • A 0.14 M
  • B 0.38 M
  • C 8 . 3 × 1 0 − 3 M
  • D 9 . 1 × 1 0 − 2 M
  • E 10 M

Q3:

Cobalt metal can be prepared by reducing cobalt(II) oxide with carbon monoxide, as shown in the equation: What concentration of C O remains in an equilibrium mixture with [ C O ] 2 = 0.100 M?

  • A 0.100 M
  • B 4 9 0 0 M
  • C 490 M
  • D 2 . 0 4 × 1 0 − 4 M
  • ENot enough information is provided.

Q4:

Carbon is reacted with water vapor at 1 0 0 0 ∘ C , establishing the equilibrium What is the concentration of C O in the equilibrium mixture if [ H O ] 2 = 0.750 M?

Q5:

Consider the equilibrium

What is the equilibrium concentration of N O 2 in 1.00 L of a solution prepared from 0.129 mol of N O 2 4 with chloroform as the solvent? Assume that the change in concentration of N O 2 4 is small enough to be neglected.

  • A 6 . 9 0 × 1 0 − 7 M
  • B 5 . 8 7 × 1 0 − 4 M
  • C 1 . 3 8 × 1 0 − 8 M
  • D 1 . 1 7 × 1 0 − 3 M
  • E 8 . 2 9 × 1 0 − 5 M

Q6:

Pure P C l 5 decomposes reversibly into P C l 3 and C l 2 : The initial concentration of P C l 5 is 2.00 M. Calculate the equilibrium concentration of C l 2 .

Q7:

What is the concentration of N O in an equilibrium mixture at 2 5 0 ∘ C that results from the reaction of 0.20 M  N O and 0.10 M  O 2 ?

  • A 0.0035 M
  • B 0.0056 M
  • C 0.012 M
  • D 0.0070 M
  • E 0.0044 M

Q8:

Consider the equilibrium

How many grams of H I are present in an equilibrium mixture containing 1.25 mol of H 2 and 63.5 g of I 2 at 4 4 8 ∘ C ?

Q9:

Consider the equilibrium

What is the minimum mass of C a C O 3 required to establish equilibrium at a certain temperature in a 6.50-L container if the equilibrium constant ( 𝐾 c ) is 0.050 for the decomposition reaction of C a C O 3 at that temperature?

Q10:

Carbon monoxide and water react at high temperature according to the equation: Under certain conditions, the equilibrium constant for this reaction ( 𝐾 c ) is 5.0.

An equilibrium mixture of the substances was found to contain 0.20 mol of C O , 0.30 mol of water vapor, and 0.90 mol of H 2 per liter of gas. How many moles of C O 2 were present in the equilibrium mixture?

Additional H 2 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 C O , 0.30 mol of water vapor, and 1.2 mol of H 2 per liter of gas. How many moles of C O 2 were there in the new equilibrium mixture?

Q11:

Antimony pentachloride decomposes according to this equation: An equilibrium mixture in a 5.00 L flask at 4 4 8 ∘ C contains 3.85 g of S b C l 5 , 9.14 g of S b C l 3 , and 2.84 g of C l 2 . 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:

This reaction follows a first-order rate law. The products are structural isomers, exhibiting the same structural formula C H O 6 1 2 6 .

In neutral solution, 𝑘 = 2 . 1 × 1 0 s−1 at 2 7 ∘ C . In the human body, the rate of this reaction is catalyzed by an enzyme, increasing the rate constant to 1 . 3 6 × 1 0 at 2 7 ∘ 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 this equation: When 0.10 mol N O 2 is added to a 1.0 L flask at 2 5 ∘ C , the concentration changes so that at equilibrium, [ N O ] 2 = 0.016 M and [ N O ] 2 4 = 0.042 M.

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

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

  • A 1 . 6 × 1 0 2
  • B 6 . 1 × 1 0 − 4
  • C0.38
  • D2.6
  • E4.2

Q14:

For the reaction 2 S O ( ) + O ( ) 2 S O ( ) 2 2 3 g g g , the concentrations at equilibrium are [ S O ] 2 = 0.90 M, [ O ] 2 = 0.35 M, and [ S O ] 3 = 1.1 M. What is the value of the equilibrium constant, 𝐾 c ?

Q15:

Iodine molecules react reversibly with iodide ions to produce triiodide ions: Before a reaction, the concentrations of I 2 and I – in a solution are both equal to 1 . 0 0 0 × 1 0 − 3 M. At equilibrium, the concentration of I 2 is 6 . 6 1 × 1 0 − 4 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: When 1.00 mol each of C H O H 2 5 and C H C O H 3 2 are allowed to react in 1.00 L of the solvent dioxane, equilibrium is established when 1 3 mol of each of the reactants remains. What is the equilibrium constant, 𝐾 c , for the reaction?

Q17:

The equilibrium constant for the reaction of nitrogen and hydrogen to produce ammonia at a certain temperature is 6 . 0 0 × 1 0 − 2 . 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 𝐾 c for the decomposition of P C l ( ) 5 g into P C l ( ) 3 g and C l ( ) 2 g is 0.0211. What is the equilibrium concentration of P C l 5 if the initial concentration of P C l 5 is 1.00 M?

Q19:

Acetic acid, C H C O H 3 2 , reacts with ethanol, C H O H 2 5 , to form water and ethyl acetate, C H C O C H 3 2 2 5 : 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.

  • A 0.22 M
  • B 0.15 M
  • C 0.45 M
  • D 0.37 M
  • E 0.60 M

Q20:

Consider the equilibrium

A 1.00 L flask is filled with 1.00 mole of H 2 and 2.00 moles of I 2 . 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 H I in the 1.00 L flask.

Q21:

Consider the equilibrium

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

  • A 2 . 1 × 1 0 − 2 M
  • B 0.15 M
  • C 1 . 5 × 1 0 − 5 M
  • D 8 . 6 × 1 0 − 6 M
  • E 4 . 9 × 1 0 − 7 M

Q22:

Consider the equilibrium

What is the equilibrium concentration of N H 4 + in a 0.25 M aqueous solution of N H 3 ?

  • A 3 . 6 × 1 0 M
  • B 1 . 8 × 1 0 M
  • C 4 . 5 × 1 0 M
  • D 2 . 1 × 1 0 M
  • E 9 . 1 × 1 0 M

Q23:

Copper(II) ions form a complex ion in the presence of ammonia: If 0.010 mol  C u 2 + is added to 1.00 L of a 1.00 M  N H 3 solution, what is the concentration of C u 2 + when the system comes to equilibrium?

  • A 6 . 7 × 1 0 − 1 5 M
  • B 2 . 1 × 1 0 − 1 6 M
  • C 1 . 1 × 1 0 − 1 5 M
  • D 2 . 4 × 1 0 − 1 6 M
  • E 7 . 0 × 1 0 − 1 6 M

Q24:

Consider the equilibrium

What is the approximate equilibrium concentration of N i 2 + when 0 . 2 5 m o l N i 2 + is added to 1.00 L of a 2 . 0 0 M N H 3 solution?

  • A 1 . 9 × 1 0 − 9 M
  • B 1 . 7 × 1 0 − 9 M
  • C 5 . 5 × 1 0 − 1 1 M
  • D 2 . 9 × 1 0 − 8 M
  • E 1 . 7 × 1 0 − 1 0 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 ?

  • A C a C O ( ) C a O ( ) + C O ( ) 3 2 s s g
  • B C l ( ) 2 C l ( ) 2 g g
  • C H ( ) + C l ( ) H C l ( ) + – a q a q a q
  • D B r ( ) + C l ( ) 2 B r C l ( ) 2 2 g g g
  • E H C O ( ) H O ( ) + C O ( ) 2 3 2 2 a q l a q

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