GCSE AQA Le Chatelier Principle

What is Le Chatelier’s Principle?

• Le Chatelier’s Principle states that if a system at equilibrium is subjected to a change (such as temperature, pressure, or concentration), the system will adjust itself to counteract that change and restore equilibrium.

• Le Chatelier’s Principle states that if a system at equilibrium is subjected to a change (such as temperature, pressure, or concentration), the system will NOT counteract the change.

How is an equilibrium represented in chemical equations?

Answer: In chemical equations, reversible reactions are indicated by using two parallel half arrows (⇌) instead of a single arrow. Eg

Formation of Hydrogen Iodide: H₂ + I₂ ⇌ 2HI

• TRUE

• FALSE

Why do some chemical reactions proceed in both forward and backward directions?

For example, the reaction of hydrogen gas and iodine vapor to form hydrogen iodide is reversible:

Forward Reaction: H₂ + I₂ ⇌ 2HI

Backward Reaction: 2HI ⇌ H₂ + I₂

• Reversible reactions can move in both directions because the products can react with each other to regenerate the reactants.

• Reversible reactions can move in the same directions because the products can react with each other to regenerate the reactants.

How does temperature affect the position of equilibrium?

• When the temperature increases, an endothermic reaction (one that absorbs heat) will shift in the forward direction to absorb the excess heat. Conversely, if the temperature decreases, an exothermic reaction (one that releases heat) will shift in the backward direction to generate more heat.

• When the temperature increases, an exothermic reaction (one that absorbs heat) will shift in the backwards direction to absorb the excess heat. Conversely, if the temperature increases, an exothermic reaction (one that releases heat) will shift in the backward direction to generate more heat.

Explain why increasing the concentration of reactants in the following reaction will shift the equilibrium position to the right: N₂ + 3H₂ ⇌ 2NH₃

• By increasing the concentration of N₂ and 3H₂ the system responds by producing more NH₃.

  This shift favors the forward reaction, leading to an increase in the concentration of NH₃.

• By increasing the concentration of N₂ and 3H₂ the system responds by producing more N₂ and 3H₂

  This shift favors the backward reaction, leading to an increase in the concentration ofN₂ and 3H₂

What happens when pressure changes in a reversible reaction involving gases?

• If the pressure increases, the equilibrium will shift toward the side with fewer moles of gas. If the pressure decreases, the equilibrium will shift toward the side with more moles of gas.

• If the pressure increases, the equilibrium will shift toward the side with more moles of gas. If the pressure decreases, the equilibrium will shift toward the side with fewer moles of gas.

2SO_2(g) + O_2(g) ⇌ 2SO_3(g) + exothermic

Removing O_2(g) will

• shift equilibrium right

• shift equilibrium left

• increase pressure

• have no change

2SO₂(g)+O₂(g) ⇌ 2SO₃(g) + Exothermic

Adding SO₃(g) will

• shift equilibrium right

• shift equilibrium left

• increase K

• have no change

2SO₂(g)+1O₂(g) ⇌ 2SO₃(g) exothermic

Increasing the volume of the container will...

• shift equilibrium right

• shift equilibrium left

• slow rate of reaction

• have no change

For N₂ + 3H₂ →2NH₃ . When pressure is increased the equilibrium shift to right. Why?

• To increase the amount of products
• To reduce the pressure, as right has less number of molecule
• K_c will increase when it is shifted to the right
• So it will increase the rate of reaction