Le Chatelier's Principle Practice Problems

The ΔH for the following reaction is −54.97 kcal/mol (−230 kJ/mol): 

2 PCl₅(s) + O₂(g) ⇌ 2 POCl₃(g) + 2 Cl₂(g)

What happens to the concentration of Cl₂ in the equilibrium mixture when the temperature is reduced?

How does elevating the temperature affect the equilibrium of the reaction between uranium and fluorine gas? 

U(s) + 3 F₂(g) → UF₆(g)            ΔH = −513.24 kcal/mol (−2147.4 kJ/mol)

The following reaction is exothermic: Sc³⁺(aq) + OH^–(aq) ⇌ ScOH²⁺(aq). Will the concentration of ScOH²⁺ increase, decrease, or remains unchanged when Tl(NO₃)₃ is added to the solution precipitating OH^–?

Consider the following reaction: Cl₂(g) + 3 F₂(g) ⇌ 2 ClF₃(g), ΔH = –78.0 kcal/mol (–326.4 kJ/mol). How will the concentration of ClF₃ at equilibrium change when F₂ is removed from the mixture?

How will the change below affect the direction of equilibrium in the following reaction between sulfur and oxygen gas?

2 S(s) + 3 O₂(g) ⇌  2 SO₃(g)       ΔH = –189.1 kcal/mol (–791.4 kJ/mol)

Sulfur trioxide (SO₃) produced is continuously collected in a separate container.

Consider the given reaction, H₂(g) + O₂(g) ⇌ H₂O₂(g) ΔH = +32.6 kcal/mol(+136.3 kJ/mol) 

When a catalyst is added, does the concentration of H₂O₂ decrease, increase, or remain the same?

True or False. At equilibrium, catalysts have no effect on the amount of reactants and products, but they do change the activation energy.

Predict the direction of the reaction when the pressure is increased by decreasing the volume of the equilibrium mixture using Le Châtelier's principle.

2 PCl₅(s) + O₂(g) ⇌ 2 POCl₃(g) + 2 Cl₂(g)

How does increasing the pressure affect the concentration of the product in the following reaction? 

H₂O₂(g) ⇌ H₂(g) + O₂(g)

How does increasing the pressure (decreasing the volume) shift the equilibrium of the reaction of uranium with fluorine gas? 

U(s) + 3 F₂(g) → UF₆(g) ΔH = −513.24 kcal/mol (−2147.4 kJ/mol)

Which of the following favors the formation of more POCl₃ at equilibrium? 

2 PCl₃(g) + O₂(g) ⇌ 2 POCl₃(g) ΔH = −130 kcal/mol 

Magnesium hydroxide is insoluble in water and is one of the solids responsible for the formation of sludge in boilers. Why is this a problem in boilers? Magnesium hydroxide is formed from the hydrolysis of magnesium chloride.

The conversion of sulfur dioxide (SO₂) to sulfur trioxide (SO₃) is a reversible reaction:

2 SO_2(g) + O_2(g) ⇌ 2 SO_3(g)

Identify what will happen to the direction of equilibrium when each of the following changes is applied:

a) More SO₃ is added to the reaction mixture.

b) O₂ is removed from the reaction mixture.

c) More SO₂ is added to the reaction mixture.

d) Neon gas is added to the reaction mixture.

Which of the following reversible reactions can be pushed towards the products' side by reducing pressure?

1. PCl_3(g) + Cl_2(g) ⇌ PCl_5(g)
2. CaCO_3(s) ⇌ CaO_(s) + CO_2(g)
3. N_2(g) + 3 H_2(g) ⇌ 2 NH_3(g)
4. CH_4(g) + H₂O_(g) ⇌ CO_(g) + 3 H_2(g)
5. 2 SO_2(g) + O_2(g) ⇌ 2 SO_3(g)

Given the following reaction at equilibrium:

2 CO₂ (g) ⇌ 2 CO (g) + O₂ (g)           ΔH° = -514 kJ

Which of the following conditions will maximize the yield of CO(g)?

Consider the following gas-phase reaction:

H₂(g) + I₂(g) ⇌ 2 HBr(g)            ΔH = –72.6 kJ

If a temperature change is applied, which of the following reaction characteristics will be affected?

I. equilibrium concentrations

II. value of the equilibrium constant