 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) Kinetic Energy Potential 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

 Draw a PE diagram. Include: axes labels, the transition state, activated complex, E a (forward and reverse), and Δ E.

CO reacts with NO 134 kJ and the Δ 2 to form CO E is -226 kJ. 2 and NO. The activation energy of the forward reaction is

  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 Step 1: NO Step 2: NO (g) (g) 3(g) + O + O 2(g) + NO 2(g)  (g)   NO 2NO 3(g) 2NO 2(g) 2(g) involves a two-step reaction mechanism: ◦ ◦ 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