Unit 10 – Kinetics

1. Unit 10 – Kinetics Obviously, atoms and molecules must collide in order for a reaction to occur. These collisions must have two characteristics: Too ____________________________ causes the molecules to simply bounce off of each other. And ________________________________ is like trying to catch a fly ball with the back of your glove.

2. Collision Theory CH2=CH2 + HCl  CH3CH2Cl

3. Activation Energy definition – energy required to ____________ Reactions may be spontaneous at a given temperature but they still need a push to get started. Think of a car in neutral on a hill – ___________________ keeps it in place but once you give it a little nudge, it starts to roll and keeps rolling.

4. Activation Energy

5. Activation Energy intermediate – transitional compound or compounds in a reaction formed when bonds are breaking and forming Reactants form the intermediate(s) which in turn breaks down to form the products. These steps are shown in a reaction mechanism. I2 2 I I + H2 H2I H2I + I  2 HI

6. Reaction Rate definition – speed at which reaction occurs The total amount of product formed is not affected by the reaction rate – it may take different amounts of time but you still get the same amount of stuff in the end. If you fly from here to Alaska while I drive, you will get there faster than me. But I will still eventually get there so we end up in the same place. In the same way, if you burn 10g of iron it makes rust almost instantly. If you leave another 10g of iron out in the weather, it will still produce the same amount of rust but it might take a few days.

7. Reaction Rate • catalyst – substance that speeds up a chemical reaction without being permanently changed itself • A catalyst _______________ the activation energy so the reaction rate increases. • It is NOT a reactant or product. • _____________________ are biological catalysts. • temperature – average kinetic energy of particles • As temperature increases, particles have more energy when they collide so reaction rate increases.

8. Reaction Rate • concentration – particles per volume • Higher concentration means that there is a greater chance that particles will collide. More particles  more collisions  faster reaction rate. • surface area – exposed surface of reactant • More surface area for the same mass means that there is a greater chance that particles will collide.

9. Reaction Rate

10. Reaction Rate Summary • catalyst – reaction rate ______________ • As temperature increases, reaction rate ______________. • As concentration increases, reaction rate ______________. • As surface area increases, reaction rate ______________. UNDERSTAND THESE TRENDS!!

11. Catalysts and Intermediates Identify the catalyst(s) and intermediate(s) in the following mechanism: OCl- + H2O  HOCl + OH- I- + HOCl  HOI + Cl- HOI + OH-  H2O + OI- Write the balanced reaction:

12. Rate Laws The rate of a reaction is directly proportional to the concentration(s) of one or more of the reactants. The rate law is the equation that relates concentration and the reaction rate. For the reaction with reactants A and B, the rate law is Rate = k[A]n[B]m where k is a constant, [A] and [B] are reactant concentrations, and n and m are orders of their respective reactants.

13. Rate Laws 2 H2(g) + 2 NO(g)  N2(g) + 2 H2O(g) For this reaction, the reaction rate is proportional to the concentrations of H2 and NO. The rate law is Rate = k[H2][NO]2 The reaction is _____ order with respect to H2 and _____ order with respect to NO. It is _____ order overall.

14. Rate Laws 2 H2(g) + 2 NO(g)  N2(g) + 2 H2O(g) Rate = k[H2][NO]2 What happens to the reaction rate if you double the concentration of a reactant? H2 NO

15. Rate Laws NO2(g) + CO(g)  NO(g) + CO2(g) The rate law of this reaction is Rate = k[NO2]2. What happens when you double the concentration of a reactant? NO2 CO