 Reactants must collide with proper orientation and sufficient energy

 Explains what happens once colliding particles react ◦ Transition state is the in-between state when reactants are being converted to products ◦ Kinetic energy is converted to potential energy (think about bouncing a basketball) Potential Energy Kinetic Energy

Negative

 Exothermic reactions- give off heat (products more stable, less potential energy)  Endothermic reactions require heat (products less stable than reactants, higher PE) Exothermic Reaction Endothermic Reaction

 CO reacts with NO 2 to form CO 2 and NO. The activation energy of the forward reaction is 134 kJ and the Δ E is -226 kJ. Draw a PE diagram. Include: axes labels, the transition state, activated complex, E a (forward and reverse), and Δ E.

 Chemical reactions typically occur as a series of steps. This series of steps that make up the overall reaction is called the reaction mechanism.  Elementary reactions are a single step in the overall reaction mechanism. ◦ Singular molecular event, such as a simple collision of atoms, molecules or ions. ◦ Cannot be broken down into further simpler steps.

 For example, the reaction 2NO (g) + O 2(g)  2NO 2(g) involves a two-step reaction mechanism: ◦ Step 1: NO (g) + O 2(g)  NO 3(g) ◦ Step 2: NO 3(g) + NO (g)  2NO 2(g)  Each step is an elementary reaction, both steps together give the overall reaction mechanism.  Notice NO 3(g) ◦ Not a product or reactant of overall reaction ◦ Produced then consumed = reaction intermediate

 Describes the number of reactant particles in an elementary step ◦ Unimolecular = one reactant  (CH 3 ) 3 CBr (aq)­  (CH 3 ) 3 C + + Br - ◦ Bimolecular = 2 reactants come together. Ex:  Step 1: NO (g) + O 2(g)  NO 3(g)  Step 2: NO 3(g) + NO (g)  2NO 2(g) ◦ Termolecular = 3 reactants  Extremely rare!!! Why?

 One step in a reaction mechanism is always much slower than the others ◦ Since it is so much slower, it determines the rate of the overall reaction.  Hence, this slow step is called the rate determining step ◦ Consider the process of making toast: slow fast

 Activation energy for rds is always higher ◦ 2 STEP REACTION MEANS 2 TRANSITION STATES AND 1 INTERMEDIATE

 Increases the rate of a reaction ◦ Homogeneous catalyst: Same phase as reactants ◦ Heterogeneous catalyst: Different phase as reactants Pd

 Not consumed! ◦ There in beginning and end of reaction ◦ Works by lowering the activation energy  Therefore, greater number of collisions have sufficient energy to react  Provide alternative reaction mechanism

 Reaction Rate  Concentration  Surface Area  Catalyst  Reactivity  Temperature  Collision Theory  Orientation  Rate Expression  Exothermic  Endothermic  Homogeneous  Heterogeneous  Kinetic Energy  Unimolecular  Rate Constant  Elementary Reaction  Mechanism  Catalyst  Rate Law  Reaction Order  Molecularity  Activation Energy  Reverse Reaction  Potential Energy  Transition State  Activated Complex  Rate Determining Step  Biomolecular  Termolecular