1. Collision Theory of Reactions A chemical reaction occurs when: Collisions between molecules have sufficient energy to break the bonds in the reactants.Collisions between molecules have sufficient energy to break the bonds in the reactants. Molecules collide with the proper orientation.Molecules collide with the proper orientation. Example: Bonds between atoms of the reactants (N 2 and O 2 ) are broken and new bonds (NO) can form.Example: Bonds between atoms of the reactants (N 2 and O 2 ) are broken and new bonds (NO) can form. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2. Collision Theory of Reactions Collision Theory of Reactions A chemical reaction does not take place if the: Collisions between molecules do not have sufficient energy to break the bonds in the reactants.Collisions between molecules do not have sufficient energy to break the bonds in the reactants. Molecules are not properly aligned.Molecules are not properly aligned. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings N 2 O 2

3. Activation Energy The activation energy is the minimum energy needed for a reaction to take place.The activation energy is the minimum energy needed for a reaction to take place. When a collision provides energy equal to or greater than the activation energy, product can form.When a collision provides energy equal to or greater than the activation energy, product can form.

4. Collision Theory in Summary Three requirements for a reaction to occur: Collision—The reactants must collide. Collision—The reactants must collide. Orientation—The reactants must align properly. Orientation—The reactants must align properly. Energy—The collision must provide the energy of activation. Energy—The collision must provide the energy of activation.

5. Reaction Rate and Temperature Increases when temperature rises because reacting molecules move faster providing more colliding molecules with energy of activation.Increases when temperature rises because reacting molecules move faster providing more colliding molecules with energy of activation.

6. Blizzard vs. the Heat Reaction: Reaction: Mg(s) + HC 2 H 3 O 2 (aq)  H 2 (g) + Mg(C 2 H 3 O 2 ) 2 (aq) acetic acid magnesium acetate

7. Reaction Rate and Concentration Reaction rate is affected by the concentration of the reactants.Reaction rate is affected by the concentration of the reactants. By adding more reactants, this increases the number of collisions.By adding more reactants, this increases the number of collisions.

8. Pioneer Porta-Stove Reaction: Reaction: CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O(g) methane

9. Reaction Rate and Catalysts A catalyst: Speeds up the rate of a reaction.Speeds up the rate of a reaction. Lowers the energy of activation.Lowers the energy of activation. Is not used up during the reaction.Is not used up during the reaction.

10. Elephant Toothpaste Reaction: Reaction: H 2 O 2 (l)  H 2 O(l) + O 2 (g) NaI hydrogen peroxide

11. Learning Check State the effect of each on the rate of reaction as: 1) increases 2) decreases3) no change A. Increasing the temperature B. Removing some of the reactants C. Adding a catalyst D. Placing the reaction flask in ice E. Increasing the concentration of one of the reactants 1 2 1 2 1

12. Learning Check Indicate the effect of each factor listed on the rate of the following reaction as: 1) increases 2) decreases 3) none 2CO(g) + O 2 (g) 2CO 2 (g) A. Raising the temperature B. Adding O 2 C. Adding a catalyst D. Lowering the temperature 1 1 1 2