Lecture_06_Mechanism%203

Lecture_06_Mechanism%203 - Mechanisms (3) For the reaction:...

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For the reaction: 2 NO + O 2 2 NO 2 Experimental rate law: rate = k[NO] 2 [O 2 ] Write the rate law expected if this reaction proceeds by the following two-step mechanism: NO + O 2 NO 3 (slow) NO 3 + NO 2 NO 2 (fast) Hypothetical rate law: rate = k[NO][O 2 ] Could this reaction proceed by this mechanism? a) yes b) no c) not enough information Clicker question
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For the reaction: 2 NO + O 2 2 NO 2 Experimental rate law: rate = k[NO] 2 [O 2 ] Write the rate law expected if this reaction proceeds by the following two-step mechanism: NO + O 2 NO 3 ( ) NO 3 + NO 2 NO 2 ( slow, rate determining ) Could this reaction proceed by this mechanism? Predicting Rate Laws for Reaction Mechanisms (3)
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For the reaction: 2 NO + O 2 2 NO 2 Experimental rate law: rate = k[NO] 2 [O 2 ] NO + O 2 NO 3 NO 3 + NO 2 NO 2 (slow) Rate law from the mechanism : rate 2 = k 2 [NO 3 ][NO] Does not match the experimental rate law Can’t have intermediates in overall rate law! Must eliminate NO 3 from the step 2 rate law. Express [NO 3 ] in terms of reactants Predicting Rate Laws for Reaction
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Unformatted text preview: Mechanisms (3) For the reaction: 2 NO + O 2 2 NO 2 Experimental rate law: rate = k[NO] 2 [O 2 ] NO + O 2 NO 3 rate 1(fwd) = k 1 [NO][O 2 ] rate 1(rev) = k-1 [NO 3 ] NO 3 + NO 2 NO 2 rate 2 = k 2 [NO 3 ][NO] Rate 1(fwd) = rate 1(rev) so k 1 [NO][O 2 ] = k-1 [NO 3 ] [NO 3 ] = (k 1 /k-1 )[NO][O 2 ] Substitute [NO 3 ] in rate law for reaction 2 Rate 2 = k 2 [NO 3 ][NO] = k 2 {k 1 /k-1 )[NO][O 2 ]}[NO] = = (k 2 k 1 /k-1 )[NO] 2 [O 2 ] Predicting Rate Laws for Reaction Mechanisms (3) Overall reactions are made of 1 or more elementary reactions In an experimental (macroscopic) reaction, you do not know the rate equation except by experiment You can write the rate equation of an elementary reaction from its stoichiometry Intermediates are not reactants nor products and do not appear in the rate equation for the overall reaction. Reaction Mechanisms Summary...
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Lecture_06_Mechanism%203 - Mechanisms (3) For the reaction:...

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