3.1.6.1 Chemical equilibria and Le Chatelier's principle

Which statement is not correct about the industrial preparation of ethanol by the hydration of ethene at 300 °C?

C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g) ∆H = –46 kJ mol^–1

• The reaction is catalysed by an acid.

• The higher the pressure, the higher the equilibrium yield of ethanol.

• The higher the temperature, the higher the equilibrium yield of ethanol.

• A low equilibrium yield of ethanol is acceptable because unreacted ethene is recycled.

Tags

NGSS.HS-PS1-5

NGSS.HS-PS1-6

For this reaction at equilibrium, which combination of temperature and pressure would give the greatest equilibrium yield of products?

W(g) + X(g) ⇌ 2Y(g) + Z(g) ∆H = +47 kJ mol^–1

• High pressure and high temperature

• High pressure and low temperature

• Low pressure and high temperature

• Low pressure and low temperature

Tags

NGSS.HS-PS1-6

The forward reaction in this equilibrium is endothermic

COCl₂ (g) ⇌ CO(g) + Cl₂ (g)

Which statement is correct?

• If the total pressure is increased at constant temperature, the proportion of COCl₂ in the equilibrium mixture will decrease

• Use of a catalyst will increase the proportion of COCl₂ in the equilibrium mixture at constant temperature and pressure

• Reducing the equilibrium concentration of CO will increase the value of the equilibrium constant

• Raising the temperature from 373 K to 473 K will increase the value of the equilibrium constant

Tags

NGSS.HS-PS1-5

NGSS.HS-PS1-6

The following equilibrium was established in a container with volume V cm³ at 393 K and 200 kPa.

M₂(g) + R(g) ⇌ RM₂(g) ΔH = +150 kJ mol⁻¹

Which change would increase the yield of RM₂?

• change the pressure to 150 kPa

• change the temperature to 293 K

• remove RM₂ as it is formed

• change the volume of the vessel to 2V cm³

Tags

NGSS.HS-PS1-6

A pale brown mixture of NO₂ and N₂O₄ is allowed to reach equilibrium in a sealed gas syringe according to the following equation.

2NO₂(g) ⇌ N₂O₄(g)

When the plunger is pushed further into the syringe the pressure increases and the mixture becomes paler in colour.

When the syringe is placed in a hot oven the mixture becomes darker in colour.

Which of the following statements is correct?

• NO₂ is brown and the forward reaction is exothermic.

• NO₂ is brown and the forward reaction is endothermic.

• NO₂ is colourless and the forward reaction is exothermic.

• NO₂ is colourless and the forward reaction is endothermic.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS1-5

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?

• A

• B

• C

• D

Tags

NGSS.HS-PS1-6

The standard enthalpy of formation, ΔH_f for O₃(g) is + 142 kJ mol^–1. In which one of the following would both the changes shown increase the amount of O₂ gas in an equilibrium mixture containing only O₂(g) and O₃(g)?

• increasing the temperature and increasing the pressure

• increasing the temperature and decreasing the pressure

• decreasing the temperature and increasing the pressure

• decreasing the temperature and decreasing the pressure

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.

Compared to the pH of solution F, the pH of solution G will be

• considerably lower.

• slightly lower.

• slightly higher.

• exactly the same.

Refer to the following reaction

H₂(g) + I₂(g) ⇌ 2HI(g) ΔH = −11 kJ mol⁻¹, ΔS = +20 J K⁻¹ mol⁻¹

Which one of the following statements is correct?

• This is a redox reaction.

• The reaction is not feasible below 298 K

• At equilibrium, the yield of hydrogen iodide is changed by increasing the pressure.

• At equilibrium, the yield of hydrogen iodide increases as the temperature is increased.

Tags

NGSS.HS-PS1-5

NGSS.HS-PS1-6

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

The equilibrium yield in all three reactions is increased when

• the pressure is increased.

• the pressure is decreased.

• the temperature is increased.

• the temperature is decreased.

Tags

NGSS.HS-PS1-6