Le Chatelier's

• Chemistry
• Secondary Education

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If a change is made to a system at dynamic equilibrium, the position of equilibrium moves to ____________ this change.

1. minimise
2. increase
3. favor

Learning Objectives

• define Le Chatelier’s principle 
• use Le Chatelier’s principle to deduce qualitatively the effects of changes in temperature, concentration, pressure or presence of a catalyst on a system at equilibrium

Le Chatelier's Principle

" If a change is made to a system at dynamic equilibrium, the position of equilibrium moves to  minimize this change. "

Factors affecting Equilibrium

• change in concentration
• change in temperature
• change in pressure 

Group Activity 1: Concentration

• Suppose you have an equilibrium established between four substances A, B, C and D.

Equilibrium Equation:

    A    +   2B             C    +    D

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Guide Questions

• What would happen if you changed the conditions by increasing the concentration of A?
• What would happen if you changed the conditions by decreasing the concentration of A?

Group Activity 2: Temperature

• For this, you need to know whether heat is given out or absorbed during the reaction. 

Assume that our forward reaction is exothermic (heat is evolved):

A + 2B      C + D        H = -250 kJ mol-1

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Δ

Guide Questions

• What would happen if you changed the conditions by increasing the temperature?
• Suppose the system is in equilibrium at 300°C, and you increase the temperature to 500°C. How can the reaction counteract the change you have made? How can it cool itself down again?
• What would happen if you changed the conditions by decreasing the temperature?

Group Activity 3: Pressure

• This only applies to reactions involving gases.

Equilibrium Equation:

   A(g) +  2B(g)       C(g) + D(g)

Σ

⇌

Guide Questions

• What would happen if you changed the conditions by increasing the pressure?
• What would happen if you changed the conditions by decreasing the pressure?
• What happens if there are the same number of molecules on both sides of the equilibrium reaction?

Rate your level of understanding of the lesson.

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