20080208 Kinetics 2 - Intro Chemistry II 030.102 Chapter 13 Spring 2008 Order of a Reaction For many(but not all reactions with a single reactant

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Intro Chemistry II – 030.102 - Chapter 13 Spring, 2008 1 Order of a Reaction For many (but not all) reactions with a single reactant, the rate is proportional to the concentration raised to a power. Rate expression for reaction a A products rate = k [A] n Important: The power n has no direct relation to coefficient a in balanced reaction. Consider the high-temp. decomposition of ethane: frequently has the form C 2 H 6 ( g ) 2 CH 3 ( g ) Rate expression has the form rate = k [C 2 H 6 ] 2 Order of a Reaction Power to which concentration is raised in the rate expression is the order of a reaction. Decomposition of N 2 O 5 is first order , decomposition of C 2 H 6 is second order . Some reactions are zeroth order . Since [A] 0 = 1, Such reactions have rates independent of concentration: rate = constant × k (zeroth-order kinetics) rate = k [CH 3 CHO] 3/2 Order of a reaction does not have to be an integer, sometimes have fractional powers. Example, thermal decomposition of acetaldehyde:
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Intro Chemistry II – 030.102 - Chapter 13 Spring, 2008 2 Example 13.1 At elevated temperatures, HI reacts according to the reaction: 2 HI( g ) H 2 ( g ) + I 2 ( g) At 443 ° C, the reaction rate depends on HI concentrations as follows: [HI] (mol L –1 ) 0.0050 0.010 0.020 Rate (mol L –1 s –1 ) 7.5 × 10 –4 3.0 × 10 –3 1.2 × 10 –2 Questions: (a) Determine order of reaction and write rate expression. (b) Calculate rate constant, and give units.
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This note was uploaded on 04/14/2008 for the course CHEMISTRY 102 taught by Professor Dagdigian during the Spring '08 term at Johns Hopkins.

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20080208 Kinetics 2 - Intro Chemistry II 030.102 Chapter 13 Spring 2008 Order of a Reaction For many(but not all reactions with a single reactant

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