1. DYNAMIC EQUILIBRIA

2. Place 2 cm3 of potassium chromate (VI) solution in a boiling tube and add sodium hydroxide solution until the solution changes colour. Observation … Explanation…

4. The forward and reverse reactions are both taking place. The reactions take place at the same speed. All reactants and products are present. The concentration of all reactants and products remain constant. DYNAMIC EQUILIBRIUM DYNAMIC EQUILIBRIUM

6. 3 H 2 (g) + N 2 (g)  2 NH 3 (g) when equilibrium lies to the left: there are more reactants than products (i.e. more H 2 and N 2 than NH 3 )

8. 3 H 2 (g) + N 2 (g)  2 NH 3 (g) when equilibrium lies to the right: there are more products than reactants (i.e. more NH 3 than H 2 and N 2 )

9. If the conditions of an equilibrium are changed, the position of the equilibrium moves to oppose the change. LE CHATELIER’S PRINCIPLE Make it hotter – equilibrium moves to cool it. Make it colder – equilibrium moves to heat it. Raise the pressure – equilibrium moves to lower it. Lower the pressure – equilibrium moves to raise it. Add a chemical – equilibrium moves to get rid of it. Remove a chemical – equilibrium moves to make more.

10. [Co(H 2 O) 6 ] 2+ + 4 Cl -  [CoCl 4 ] 2- + 6 H 2 O pink blue THE EFFECT OF CONCENTRATION add Cl - add H 2 O

11. THE EFFECT OF TEMPERATURE forward reaction is exothermic: – 76 kJ mol -1 reverse reaction is endothermic : + 76 kJ mol -1 3 H 2 (g) + N 2 (g)  2 NH 3 (g) If the temperature is raised – the equilibrium moves to cool down by moving in the endothermic direction. If the temperature is lowered – the equilibrium moves to heat up by moving in the exothermic direction.

12. THE EFFECT OF TEMPERATURE forward reaction is endothermic reverse reaction is exothermic [Co(H 2 O) 6 ] 2+ + 4 Cl -  [CoCl 4 ] 2- + 6 H 2 O pink blue heat up the equilibrium mixture: cool down the equilibrium mixture:

13. high temperature low temperature [Co(H 2 O) 6 ] 2+ + 4 Cl -  [CoCl 4 ] 2- + 6 H 2 O forward endothermic pink blue

14. THE EFFECT OF TEMPERATURE forward reaction is exothermic reverse reaction is endothermic 2 NO 2 (g)  N 2 O 4 brown colourless heat up the equilibrium mixture: cool down the equilibrium mixture:

15. high temperature low temperature 2 NO 2  N 2 O 4 forward exothermic brown colourless

16. THE EFFECT OF PRESSURE 3 H 2 (g) + N 2 (g)  2 NH 3 (g) 4 molecules 2 molecules More pressure Less pressure

17. THE EFFECT OF PRESSURE 2 NO 2 (g)  N 2 O 4 (g) brown colourless 2 molecules 1 molecule More pressure Less pressure

19. CATALYSTS FACTORS AFFECTING THE POSITION OF EQUILIBRIUM EaEa MAXWELL-BOLTZMANN DISTRIBUTION OF MOLECULAR ENERGY EXTRA MOLECULES WITH SUFFICIENT ENERGY TO OVERCOME THE ENERGY BARRIER MOLECULAR ENERGY NUMBER OF MOLECUES WITH A PARTICULAR ENERGY Catalysts work by providing an alternative reaction pathway involving a lower activation energy.

20. CATALYSTS An increase in temperature is used to speed up chemical reactions but it can have an undesired effect when the reaction is reversible and exothermic. In this case you get to the equilibrium position quicker but with a reduced yield because the increased temperature moves the equilibrium to the left. In many industrial processes a compromise temperature is used (see Haber and Contact Processes). To reduce the problem one must look for a way of increasing the rate of a reaction without decreasing the yield i.e. with a catalyst. FACTORS AFFECTING THE POSITION OF EQUILIBRIUM

21. CATALYSTS An increase in temperature is used to speed up chemical reactions but it can have an undesired effect when the reaction is reversible and exothermic. In this case you get to the equilibrium position quicker but with a reduced yield because the increased temperature moves the equilibrium to the left. In many industrial processes a compromise temperature is used (see Haber and Contact Processes). To reduce the problem one must look for a way of increasing the rate of a reaction without decreasing the yield i.e. with a catalyst. Adding a catalyst DOES NOT AFFECT THE POSITION OF EQUILIBRIUM. However, it does increase the rate of attainment of equilibrium. This is especially important in reversible, exothermic industrial reactions such as the Haber or Contact Processes where economic factors are paramount. FACTORS AFFECTING THE POSITION OF EQUILIBRIUM