10-16-08[lecture13]ec - Chem 116 Student Notes(EC Lecture...

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Unformatted text preview: Chem 116 Student Notes October 16, 2008 (EC) Lecture 13: Collision Theory and Reaction Mechanisms Determining Rate Laws: rate = k [A]m [B]n 1) Find m and n a) b) or or 2) Find k a) Clicker Question: A(g) 2C(g) 1 unit of A makes 2 units of C, so C is appearing 2x as fast as A is disappearing (or A is disappearing ½ as fast as C is appearing). ½(6.2x10‐2) = 3.1x10‐2, therefore ‐3.1x10‐2 is the answer (negative sign for disappearing) Half­life: time it takes for ½ of the substance to react 1. time of ½ life only depends on the k value (rest are constants) a. [At] is going to become ½ [Ao] i. =2 b. ln[At]=ln[Ao]‐k t i. ii. K thalf‐life = ln2 c. thalf‐life = 2. a. # of half‐lives b. t = time elapsed c. [Aend] [Astart] Causes of Reaction Rates 1. Concentration Rates a. [A] and [B] i. More collisions more reactions 2. Temperature a. T i. More collisions more reactions 3. Frequency Factor (% of collisions that happen at the right orientations of the reactants to create products) a. A i. Higher % more reactions 4. Activation Energy (Energy required to start off the reaction) a. Ea i. Lower Ea more reactons Summed up by: 5. Can be rewritten by: 6. 7. Therefore: 8. ...
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