OCR A2 Chemistry Le Chatelier's Principle

OCR A2 Chemistry Le Chatelier's Principle

1. Dynamic Equilibrium

   • The equilibrium which exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction
   • A chemical system is in dynamic equilibrium when:
     • The concentrations of the reactants and the products remain the same
     • The rate of the forward reaction is equal to that of the reverse reaction

2. The effect of pressure on equilibrium

   • Changing the pressure only changes the position of equilibrium if there are gases present
   • Increasing the pressure will shift the position of equilibrium to the side with the fewer gas molecules
   • Decreasing the pressure will shift the position of the equilibrium to the side with a greater number of gas molecules

3. The effect of temperature on equilibrium

   • Increasing the temperature shifts the position of the equilibrium in the endothermic direction in order to minimise the temperature increase and absorb energy
   • Decreasing the temperature shifts the position of the equilibrium in the exothermic direction in order to minimise the temperature decrease and replace heat energy

4. Le Chatelier's principle states:

   • When a system in dynamic equilibrium is subjected to change the position of the equilibrium will shift to minimise the change

5. The effect of concentration on equilibrium

6. The effect of a catalyst on equilibrium