four (4) times faster than it was at 323 K, what is the activation energy?
1. The sum of Steps 1 and 2 must yield the overall reaction. 2. NO 3 is called a reaction intermediate. It is not a reactant nor a product. NO 2 + CO NO + CO 2 k 1 k 2 65
A Molecular Representation of the Elementary Steps in the Reaction of NO 2 and CO 66
These two steps are very unlikely to proceed at the same rate. One will be much slower than the other. It is the RATE DETERMINING STEP. NO 2 + CO NO + CO 2 67
rate = k[NO 2 ] 2 A possible reaction mechanism: Step 1: NO 2 + NO 2 NO 3 + NO slow Step 2: NO 3 + CO NO 2 + CO 2 fast NO 2 + CO NO + CO 2 68
Reaction Mechanisms • Sequence of steps by which reactants turn to products For Mechanism to be valid: • Sum of steps must total to overall reaction • Must agree with observed rate law 69
Rate-Determining Step • Slow step in the mechanism • Step that determines the rate of reaction and the rate law 70
71 ELEMENTARY STEPS RATE LAW DEPENDS ON MOLECULARITY (i.e., the # of species that must collide to produce the reaction indicated by that step.) UNIMOLECULAR STEP: Rxn. involving one molecule; always 1 st order.
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