1. ENTHALPY Activation energy, the activated complex, and the effect of a catalyst

2. Learning Objectives The activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction. The activation energy is the energy required by colliding molecules to form an activated complex. The activation energy can be calculated from potential energy diagrams. The effect of a catalyst can be explained in terms of alternative reaction pathways with lower activation energy. A potential energy diagram can be used to show the effect of a catalyst on activation energy.

3. ACTIVATION ENERGY

4. Reaction Progress Energ y Reactants Products

5. Reaction Progress Energ y Reactants Products HH EAEA

6. Reaction Progress Energ y Reactants Products HH

7. Reaction Progress Energ y Reactants Products HH

8. Reaction Progress Energ y Reactants Products HH EAEA

9. Reaction Progress Energ y Reactants Products HH EAEA What happens here?

10. THE ACTIVATED COMPLEX

11. Reactant A

12. Reactant B

16. Activated complex

20. Product C

21. Reaction Progress Energ y Reactants A + B Product C HH EAEA Activated Complex

22. THE EFFECT OF A CATALYST

23. MOLECULAR ENERGY EaEa NUMBER OF MOLECUES WITH A PARTICULAR ENERGY

24. EaEa EXTRA MOLECULES WITH SUFFICIENT ENERGY TO OVERCOME THE ENERGY BARRIER MOLECULAR ENERGY NUMBER OF MOLECUES WITH A PARTICULAR ENERGY

25. Reaction Progress Energ y Reactants Products HH Effect of catalyst Without catalyst EAEA

26. Reaction Progress Energ y Reactants Products HH Effect of catalyst With catalyst

27. Reaction Progress Energ y Reactants Products HH Effect of catalyst With catalyst EAEA

28. Reaction Progress Energ y Reactants Products HH Effect of catalyst Without catalyst EAEA

29. Reaction Progress Energ y Reactants Products HH Effect of catalyst With catalyst EAEA

30. Reaction Progress Energ y Reactants Products HH Effect of catalyst Without catalyst With catalyst EAEA EAEA