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
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