WARM UP List 3 things you can do to a chemical reaction to increase the rate.

Reaction Mechanisms Chemistry II

Elementary Steps Reactions occur in a series of small steps –Reaction mechanism is the sequence of these elementary steps –Ex: 2 NO (g) + O 2(g)  2 NO 2(g) –2 NO  N 2 O 2 –N 2 O 2 + O 2  2 NO 2

Elementary Steps –Ex: 2 NO (g) + O 2(g)  2 NO 2(g) –2 NO  N 2 O 2 –N 2 O 2 + O 2  2 NO 2 –Intermediates are formed and used (ex: N 2 O 2 ) Catalysts enter and re-appear, while intermediates are produced and disappear

Elementary Steps –Necessary because it is much more likely for molecules to meet 2-at-a-time in a chain, rather than 8-at-a-time all at once

Molecularity # of reacting molecules in an elementary step –Unimolecular: one reactant –Bimolecular: two reactants –Termolecular: more than 2 (rare)

Rate Determining Step Elementary step that determines rate –The slowest “car”

Rate Determining Step Concentration of reactants in rate- determining step gives us the rate law –Ex: 2 NO (g) + O 2(g)  2 NO 2(g) 2 NO  N 2 O 2 N 2 O 2 + O 2  2 NO 2 If rate = k [NO], step 1 is rate-determining

WRAP UP 1)If the rate law for the reaction, 2 NO (g) + O 2(g)  2 NO 2(g), is rate = k[NO][O 2 ] 3, which is the rate- determining step? How do you know this? Step 1) 2 NO  N 2 O 2 Step 2) N 2 O 2 + O 2  2 NO 2

WARM UP “It’s not the load that breaks you down – it’s the way you carry it.” 1)Do you agree with this? Why? 2)How does this apply to your own life?

WRAP UP Which type of elementary step is more common – bimolecular or termolecular? Why?