2. Reaction Rate How Fast Does the Reaction Go

3. Collision Theory l In order to react molecules and atoms must touch each other. l They must hit each other hard enough to react. l Anything that increase these things will make the reaction faster.

4. Energy Reaction coordinate Reactants Products

5. Energy Reaction coordinate Reactants Products Activation Energy - Minimum energy to make the reaction happen

6. Energy Reaction coordinate Reactants Products Activated Complex or Transition State

7. Energy Reaction coordinate Reactants Products Overall energy change

8. Things that Effect Rate l Temperature l Higher temperature faster particles. l More and harder collisions. l More concentrated closer together the molecules. l Collide more often

9. Things that Effect Rate l Particle size l Molecules can only collide at the surface. l Smaller particles bigger surface area. l Smallest possible is molecules or ions. l Dissolving speeds up reactions.

10. Things that Effect Rate l Catalysts- substances that speed up a reaction without being used up.(enzyme). l Speeds up reaction by giving the reaction a new path. l The new path has a lower activation energy. l More molecules have this energy. l The reaction goes faster. l Inhibitor- a substance that blocks a catalyst.

11. Energy Reaction coordinate Reactants Products

12. Pt surface HHHH HHHH l Hydrogen bonds to surface of metal. l Break H-H bonds Catalysts

13. Pt surface HHHH Catalysts C HH C HH

14. Pt surface HHHH Catalysts C HH C HH l The double bond breaks and bonds to the catalyst.

15. Pt surface HHHH Catalysts C HH C HH l The hydrogen atoms bond with the carbon

16. Pt surface H Catalysts C HH C HH HHH

17. Reaction Mechanism l Reaction mechanism is a description of how the reaction really happens. l An intermediate is a product that immediately gets used in the next reaction.

18. + This reaction takes place in three steps

19. + EaEa First step is fast Low activation energy

20. Second step is slow High activation energy + EaEa

21. Second step is rate determining

22. Energy l Substances tend react to achieve the lowest energy state. l Most chemical reactions are exothermic. l Doesn’t work for things like ice melting. l An ice cube must absorb heat to melt, but it melts anyway. Why?

23. Entropy l The degree of randomness or disorder. l The first law of thermodynamics. The energy of the universe is constant. l The second law of thermodynamics. The entropy of the universe increases in any change. l Drop a box of marbles. l Watch your room for a week.

24. Entropy Entropy of a solid Entropy of a liquid Entropy of a gas l A solid has an orderly arrangement. l A liquid has the molecules next to each other. l A gas has molecules moving all over the place.

25. Entropy increases when... l Reactions of solids produce gases or liquids, or liquids produce gases. l A substance is divided into parts -so reactions with more reactants than products have an increase in entropy. l the temperature is raised -because the random motion of the molecules is increased. l a substance is dissolved.

26. Spontaneous reaction l Reactions that will happen. l Nonspontaneous reactions don’t. l Two factors influence. l Enthalpy (heat) and entropy(disorder).

27. Two Factors l Exothermic reactions tend to be spontaneous. Reactions where the entropy of the products is greater than reactants tend to be spontaneous..

28. Equilibrium l Eventually you reach a point where the reverse reaction is going as fast as the forward reaction. l This is dynamic equilibrium. l The rate of the forward reaction is equal to the rate of the reverse reaction. l The concentration of products and reactants stays the same, but the reactions are still running.

29. Equilibrium l Equilibrium position- how much product and reactant there are at equilibrium. l Shown with the double arrow. l Reactants are favored l Products are favored l Catalysts speed up both the forward and reverse reactions so don’t affect equilibrium position.

30. Measuring equilibrium l At equilibrium the concentrations of products and reactants are constant. l We can write a constant that will tell us where the equilibrium position is. l K eq equilibrium constant l K eq = [Products] coefficients [Reactants] coefficients l Square brackets [ ] means concentration in molarity (moles/liter)

31. Writing Equilibrium Expressions l General equation aA + bB cC + dD l K eq = [C] c [D] d [A] a [B] b l Write the equilibrium expressions for the following reactions. l 3H 2 (g) + N 2 (g) 2NH 3 (g) l 2H 2 O(g) 2H 2 (g) + O 2 (g)

32. What it tells us l If K eq > 1 Products are favored l If K eq < 1 Reactants are favored

33. LeChâtelier’s Principle l If something is changed in a system at equilibrium, the system will respond to relieve the stress. l Three types of stress are applied.

34. Changing Concentration l If you add reactants (or increase their concentration). l The forward reaction will speed up. l More product will form. l Equilibrium “Shifts to the right” Reactants  products

35. Changing Concentration l If you add products (or increase their concentration). l The reverse reaction will speed up. l More reactant will form. l Equilibrium “Shifts to the left” Reactants  products

36. Changing Concentration l If you remove products (or decrease their concentration). l The forward reaction will speed up. l More product will form. l Equilibrium “Shifts to the right” Reactants  products

37. Changing Concentration l If you remove reactants (or decrease their concentration). l The reverse reaction will speed up. l More reactant will form. l Equilibrium “Shifts to the left”. Reactants  products l Used to control how much yield you get from a chemical reaction.

38. Changing Temperature l Reactions either require or release heat. l Endothermic reactions go faster at higher temperature. l Exothermic go faster at lower temperatures. l All reversible reactions will be exothermic one way and endothermic the other.

39. Changing Temperature l As you raise the temperature the reaction proceeds in the endothermic direction. l As you lower the temperature the reaction proceeds in the exothermic direction. Reactants + heat  Products at high T Reactants + heat  Products at low T

40. Changes in Pressure l As the pressure increases the reaction will shift in the direction of the least gases. At high pressure 2H 2 (g) + O 2 (g)  2 H 2 O(g) At low pressure 2H 2 (g) + O 2 (g)  2 H 2 O(g)