Warm Up: On the back of HW set 16-3, use the enthalpies of formation listed below to determine  H for the reaction: 2 H 2 O 2 (aq)  2 H 2 O (l) + O 2 (g) SubstanceEnthalpy of Formation (kJ/mol) H 2 O 2 (aq)-191 H 2 O (l)-286 O 2 (g)0

Chemical Reactions and Energy What causes a chemical reaction to occur? –Reactant molecules must collide with a favorable orientation and with enough energy to disrupt the bonds of the reactants to form to the products. This is known as collision theory. Minimum energy required to cause a chemical reaction to occur is called activation energy (E a ). –The value of E a depends on the particular reaction.

Particle Collisions

In the brief interval of bond breakage and bond formation, the collision complex is in a transition state. –A transitional structure that results from an effective collision and that persists while old bonds are breaking and new bonds are forming is called an activated complex. –The activated complex is a very short-lived molecular complex.

Reaction Energy Diagrams Graph used to represent what occurs during a chemical reaction in terms of energy and particles.

Catalysts A catalyst is a substance that increases the rate of a chemical reaction without itself being permanently consumed. A catalyst provides an alternative energy in which the energy barrier between reactants and products is lowered. A catalyst forms an alternative activated complex that requires a lower activation energy. Catalysts are reaction specific.

What Do You Think? a)How does the catalyst affect the magnitude of the activation energy? b)Does the catalyst change the amount of energy released in the reaction? c)Along which of the two reaction paths are reactants converted more rapidly to products?

Outcome Sentences After reflecting on today’s lesson, complete three of the sentence starters in your chemistry journal entry for today. Sentence Starters –I’ve learned… –I was surprised… –I’m beginning to wonder… –I would conclude… –I now realize that…