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Announcements Welcome back! Email me this week if your Exam #2 score was <70 FYI- Exam #3 is one week from Friday (April 23rd) Review session: Wednesday, April 21st @ 5:00pm

Graphical Form Two point form The Arrhenius equation is used to determine the activation energy (Ea) from experimental data Graphical Form Two point form

Using the graphical method to find Ea

Example: A reaction triples its rate when the temperature increases from 25 oC to 37 oC. What is the activation energy?

Example: A reaction has Ea = 75 kJ/mol. If k = 1 Example: A reaction has Ea = 75 kJ/mol. If k = 1.50 x 10-3 at 25 oC, what is k at 50 oC?

A reaction mechanism is the pathway from reactants to products Elementary step: a discrete step along a reaction pathway Overall reaction: the sum of a series of elementary steps “Molecularity”: the number of molecules involved in a step Unimolecular Biomolecular Termolecular (very rare)

A catalyst can speed up a reaction Intermediate: Produced in one step as a product and used as a reactant in another Catalyst: Used as a reactant in one step and produced as a product in another

Example: Identifying overall reaction and intermediates/catalysts

What intermediate(s) occur in the following reaction? N2O2 H2O N2O2 and H2 N2O2 and H2O N2O and H2O N2O2 and N2O There are none

What acts as a catalyst in the following reaction? N2O2 H2 N2O H2O There is no catalyst

The rate of an overall reaction is the rate of its slowest (rate determining) step Each elementary step has its own rate The rate determining step is the step with the slowest rate

The rate law for an elementary step is given by the equation for that step Molecularity Rate Equation A → product Unimolecular Rate= k[A] A + B → product Biomolecular Rate= k[A][B] A + A → product Bimolecular Rate= k[A]2 2A + B → product Termolecular Rate= k[A]2[B]

Proposed mechanism 1: Proposed mechanism 2: Step 1: H2 + ICl → HI + HCl (slow) Step 2: ICl + HCl → HI + Cl2 Sum Rate Step 1 Step 2 Overall Proposed mechanism 2: Step 1: H2 + ICl → HCl + HI (slow) Step 2: HI+ ICl → HCl + I2 Sum Rate Step 1 Step 2 Overall How to determine if a proposed reaction mechanism is “reasonable” H2 + 2ICl → 2HCl + I2