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Lecture 6 - Chemical Kinetics

Lecture 6 - Chemical Kinetics - Reaction Mechanism NO2(g...

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Reaction Mechanism NO 2 (g) + CO(g) NO(g) + CO 2 (g) Overall rxn rate = k[NO 2 ] 2 Step (1) NO 2 (g) + NO 2 (g) NO 3 (g) + NO(g) rate = k 1 [NO 2 ] 2 Step (2) NO 3 (g) + CO(g) NO 2 (g) + CO 2 (g) rate = k 2 [NO 3 ][CO] NO 2 (g) + CO(g) NO(g) + CO 2 (g) rate = k[NO 2 ] 2 slow fast A I P slow fast
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[ ] [ ] [ ] ( ) ( ) [ ] EQ t k k EQ A e A A t A + = + 1 1 0 ) ( [ ] EQ A [ ] EQ B Kinetics of Reversible Elementary Step A B k 1 k -1 [ ] [ ] [ ] B k A k dt A d 1 1 + = [ ] [ ] ( ) ( ) t k k EQ e B t B 1 1 1 ) ( + = [ ] [ ] [ ] B k A k dt B d 1 1 = A B k 1 k -1 exchange rate = k 1 + k -1 [ ] [ ] 1 1 = = k k A B K EQ EQ eq [A] 0 – [A] EQ relaxation time = 1 1 1 + k k
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A B k 1 k -1 Initial conditions: [A] = [A] 0 and [B] = 0 When reaction proceeds halfway to equilibrium [ ] [ ] ( ) [ ] [ ] ( ) EQ EQ A A A A = 0 5 . 0 , [ ] [ ] { } [ ] [ ] { } [ ] [ ] ( ) [ ] [ ] 2 1 5 . 0 0 0 0 = = EQ EQ EQ EQ A A A A A A A A [ ] [ ] { } [ ] [ ] { } ( ) t k k A A A A EQ EQ 1 1 0 ln + = ( ) 2 / 1 1 1 2 1 ln t k k + = ( ) 2 / 1 1 1 2 ln t k k + + = 1 1 2 / 1 2 ln + = k k t . [ ] [ ] [ ] [ ] t k k A A A A EQ EQ ) ( ln 1 1 0 + = Half-life (t 1/2 ) of Reversible First-order Reaction [A] EQ t 1/2 [A] 0 – [A] EQ [B] EQ
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