Factors that Affect the Rate of Reaction.

Alfred Nobel amassed a fortune during his lifetime from his 355 inventions, dynamite is the most famous. In 1888, opened a newspaper to read his own obituary. As it was Alfred's brother Ludvig who had died, the obituary was eight years premature. Nobel s reflection on his life’s impacts inspired him to leave his fortune to create prizes for the"greatest benefit on mankind" in physics, chemistry, peace, physiology or medicine, and literature. Nobel's instructions named a Norwegian Nobel Committee to award the Peace Prize. Now, Norway's Nobel Committee was responsible for awarding the Nobel Peace Prize and the Swedish institutions retained responsibility for the other prizes. nitroglycerin

3 Table salt is an ionic compound  transfer electrons from the metal to the non-metal to form an easily dissociated compound (just add water) ◦ Sodium chloride, NaCl (s), is a comprising sodium ions, Na +, and chloride ions, Cl –. ◦ Cation (+) and anion (-) attract like magnets

4 Free energy (if you get energy or put it in) can be used to predict whether a process is spontaneous (favorable) or nonspontaneous (not favorable) ΔG < 0 spontaneous spontaneous ΔG > 0 nonspontaneous nonspontaneous Which one would you favor?

5  The same principles can be applied to chemical reactions to predict whether they are favorable or not: FreeEnergy(G)FreeEnergy(G) Progress of reaction Α → B AA ΒΒ ΔG < 0 spontaneous spontaneous FreeEnergy(G)FreeEnergy(G) Progress of reaction Α → B AA ΒΒ ΔG > 0 nonspontaneous nonspontaneous

6  Just because a reaction is spontaneous, does not mean that it will occur at an observable rate. Diamond and graphite are two different forms of pure carbon. The reaction that converts diamond to graphite is actually a favorable one FreeEnergy(G)FreeEnergy(G) Progress of reaction Diamond → Graphite DiamondDiamond GraphiteGraphite ΔG < 0 spontaneous spontaneous Why can Beer’s say diamonds are forever?

7  There is is a hill that for most reactions the reactants must climb and go over to before they can go on to become product. FreeEnergy(G)FreeEnergy(G) Progress of reaction Α → B AA ΒΒ Products Reactants

8 The amount of energy you need to put is the activation energy, E act. ◦ The activation energy has no effect on the overall change in the free energy for the reaction. FreeEnergy(G)FreeEnergy(G) Progress of reaction Α → B AA ΒΒ ΔG < 0 spontaneous spontaneous E act > 0 Products Reactants Energy you put-in Energy you get (gain)

10 So before we go calling DeBeers can you think of an anwers to why the reaction that converts diamond to graphite is actually a favorable one – but it doesn’t happen often (or quickly) FreeEnergy(G)FreeEnergy(G) Progress of reaction Α → B AA ΒΒ ΔG < 0 spontaneous spontaneous E act > 0 Products Reactants

11  The activation energy for the conversion of diamond to graphite is very, very,very high. FreeEnergy(G)FreeEnergy(G) Progress of reaction ΔG < 0 spontaneous spontaneous E act > 0 Diamond → Graphite DiamondDiamond GraphiteGraphite

12  The reaction rate (speed) of a reaction is determined by the height of the hill. ◦ The higher the activation energy, the slower the reaction rate. But WHY, How is this connected to the Nature of the reactants? What takes energy to make and break?

13 We can estimate by: Counting the number of bonds being broken and made 5C 2 O MnO H + → 10CO 2 + 2Mn H 2 O Many bonds need to be broken and made =slow reaction. Fe 2+ + Ce 4+ → Fe 3+ + Ce 3+ This is a fast reaction because no bonds are being broken ( only 1 electron is being transferred) Reactants with strong bonds = more Ea=slower reaction rate Reactants with weak bonds =smaller Ea= faster reaction rate

15 We know two ways to speed up the reaction rate. We just haven't thought about them as overcoming activation energies but now we will. ◦ Increase the temperature of the reactant molecules. This increases the kinetic energy, which increases the motion of the reactant molecules. This increases the frequency with which they will collide with one another to react. ◦ Increase the concentration of the reactant molecules. This increases the number of reactant molecules. This also increases the frequency with which they will collide with other reactant molecules.

16  We will dive into collision theory next class for now: Increase the temperature of the reactant molecules. This increases the kinetic energy, which increases the motion of the reactant molecules. This increases the frequency with which they will collide with one another to react. Increase the concentration of the reactant molecules. This increases the number of reactant molecules. This also increases the frequency with which they will collide with other reactant molecules.

17  There is a third way to speed up the reaction rate and that is to lower the height of the hill. ◦ This is done using catalysts, which provide an alternative pathway over the hill for the reactants. FreeEnergy(G)FreeEnergy(G) Progress of reaction Α → B AA ΒΒ ΔG < 0 spontaneous spontaneous E act > 0 without catalyst - with catalyst E act > 0 without catalyst - with catalyst

18  Catalysts speed up a reaction, by lowering the activation energy but are not produced or consumed in a reaction. ◦ In the reaction equation, their presence in indicated above or below the reaction arrow. They have not effect on the change in free energy for the reaction, ΔG. They cannot be used to make an unfavorable reaction favorable. If the number of bonds broken/made remains the same how might catalysts do this?

19  In biological systems, catalysts are called enzymes. ◦ Most enzymes are proteins. ◦ Nearly every reaction that takes place in a living cell has an enzyme associated with. ◦ Enzymes bind the reactants, facilitate the reaction, and then release the products. We will revisit ENZYMES over and over and over again! They are fascinating! ENZYMES can do what chemical factories do with little /no effort! Remember the Harper-Borsh process for ammonia. We will revisit ENZYMES over and over and over again! They are fascinating! ENZYMES can do what chemical factories do with little /no effort! Remember the Harper-Borsh process for ammonia.