3.1.6.2 Equilibrium constant Kc for homogeneous systems

Hydrogen can be produced by this reaction.

CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)

In an experiment 4.20 mol of carbon monoxide were mixed with 2.00 mol of steam. When the reaction reached equilibrium, 1.60 mol of hydrogen had been formed.

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

• 0.30

• 0.41

• 1.54

• 2.46

Tags

NGSS.HS-PS1-6

When one mole of ammonia is heated to a given temperature, 50% of the compound dissociates and the following equilibrium is established.

NH₃(g) ⇌ 0.5N₂(g) + 1.5H₂(g)

What is the total number of moles of gas present in this equilibrium mixture?

• 1.5

• 2.0

• 2.5

• 3.0

A and B react together in this reversible reaction.

A + 3B ⇌ C + 2D

A mixture of 10 mol of A and 10 mol of B were left to reach equilibrium. The equilibrium mixture contained 4 mol of B.

What is the total amount, in moles, of substances in the equilibrium mixture?

• 14

• 16

• 18

• 20

Tags

NGSS.HS-PS1-7

Hydrogen is produced by the reaction of methane with steam. The reaction mixture reaches a state of dynamic equilibrium.

CH₄(g) + H₂O(g) ⇌ CO(g) + 3H₂(g) ∆H = +206 kJ mol⁻¹

Which of the following shows how the equilibrium yield of hydrogen and the value of the equilibrium constant are affected by the changes shown?

• Change: Increase pressure

  Effect on equilibrium yield of H₂(g): decrease

  Effect on value of K_c: decrease

• Change: Add a catalyst

  Effect on equilibrium yield of H₂(g): increase

  Effect on value of K_c: no effect

• Change: Increase temperature

  Effect on equilibrium yield of H₂(g): increase

  Effect on value of K_c: increase

• Change: Remove CO(g) as formed

  Effect on equilibrium yield of H₂(g): increase

  Effect on value of K_c: increase

Tags

NGSS.HS-PS1-6

Use the information about the following solutions to answer the question below.

Solution F: This is a mixture of 1 mol of propanoic acid, 1 mol of methanol and 2 mol of water.

Solution G: This was originally the same mixture as solution F but it has been left to reach equilibrium.

Solution G was found to contain 0.5 mol of propanoic acid. Which one of the following is the value of the equilibrium constant (K_c) for the following equilibrium?

propanoic acid + methanol ⇌ methyl propanoate + water

• 0.2

• 1

• 5

• 10

Ethanoic acid reacts with ethanol in a reversible reaction represented by the equation below.

In an experiment 3.0 mol of ethanoic acid were mixed with 1.0 mol of ethanol and when the reaction had reached equilibrium 0.9 mol of water had been formed.

CH₃COOH(l) + C₂H₅OH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l)

The equilibrium constant for the reaction under these conditions is

• 0.20

• 0.23

• 3.9

• 4.3

Ethanoic acid reacts with ethanol in a reversible reaction represented by the equation below.

In an experiment 3.0 mol of ethanoic acid were mixed with 1.0 mol of ethanol and when the reaction had reached equilibrium 0.9 mol of water had been formed.

CH₃COOH(l) + C₂H₅OH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l)

The percentage of ethanoic acid converted into the ester CH₃COOC₂H₅ in this reaction is

• 22.5%

• 30%

• 43%

• 90%

The data below refer to the industrial production of nitric acid from ammonia.

Possible units for the equilibrium constant, K_c, for reaction 2 are

• mol⁻² m⁶

• mol⁻¹ dm³

• no units

• mol dm⁻³

Use the information below to answer this question.

A saturated solution of magnesium hydroxide, Mg(OH)₂, contains 0.1166 g of Mg(OH)₂ in 10.00 dm³ of solution. In this solution the magnesium hydroxide is fully dissociated into ions.

The equilibrium constant expression for the dissolving of magnesium hydroxide is K = [Mg²⁺] [OH⁻]². In a saturated solution of Mg(OH)₂ at a different temperature, the concentration of hydroxide ions is 1.0 × 10⁻³ mol dm⁻³.

Which one of the following has the correct value and units for K under these conditions?

• 1.0 × 10⁻⁶ mol² dm⁻⁶

• 5.0 × 10⁻⁷ mol² dm⁻⁶

• 1.0 × 10⁻⁹ mol³ dm⁻⁹

• 5.0 × 10⁻¹⁰ mol³ dm⁻⁹

The ester methyl ethanoate is hydrolysed as shown in the following equation.

A 3 mol sample of methyl ethanoate was mixed with 3 mol of water and left to reach equilibrium at 298 K. The equilibrium yield of ethanoic acid was 2 mol. The value of K_c for this reaction at 298 K is

• 
• 
• 2

• 4