Chapter 13 notes

Chapter 13 notes - Chapter 13 Objectives (Kinetics) 1. The...

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Chapter 13 Objectives (Kinetics) Spring 2084/Chem 0970 1. The rate of chemical reactions. a) Various methods have been developed to measure how fast or slow reactions occur. b) The study of rate of reaction and the factors that influence these rates are called kinetics. c) Most reactions run fastest at the beginning of reaction when reactant concentrations are highest. d) Virtually all chemical reactions run faster when the temperature is increased. e) Rate is change of concentration per unit time; [Cl 2 ] represents molarity of Cl 2 and dt ] Cl [ d 2 - is the expression for rate of disappearance of Cl 2 . Example 1: In Cl 2 + 2 NO 2 NOCl, if the rate = dt ] Cl [ d 2 - , does NO disappear at the same rate as Cl 2 ? f) The rate of appearance of some product, e.g. , NOCl is dt ] NOCl [ d + . g) The average rate of appearance or disappearance can be determined by graphing [ ] vs. time and the instantaneous rate is equal to the tangent to the curve. h) Rate can be measured by monitoring pressure changes, color intensity, and other methods. 2. Chemical reactions have a rate law. a) For a reaction a A + b B → c C + d D, the rate law is written rate = k [A] x [B] y , where x and y are usually 0, 1, 2, -1 or even 1/2 and are not necessarily = to a and b and k is a specific rate constant (different for each reaction). Note: x and y are related to the ‘order’ of reaction. If x = 1, we say the reaction is first order in A. If x = 2, the reaction is second order in B and third order overall. Example 2: Write the general form of the rate law for: a) 2 CO (g) + O 2(g) 2 CO 2(g) b) H 2(g) + Cl 2(g) 2 HCl (g) b) In general, experiments are run at constant temperature to measure a change in rate when one reactant concentration changes and the others are constant. Consider A 2(g) + B 2(g) 2 AB (g)
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Chapter 13 Objectives (Kinetics) Spring 2084/Chem 0970 Run 1 [A 2 ] [B 2 ] Rate 1 0.10 0.10 2.0 × 10 -3 2 0.20 .010 8.0 × 10 -3 Remember: rate = k [A 2 ] m [B 2 ] m . Example 3: Can you deduce the value of m? Strategy:
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This note was uploaded on 04/07/2008 for the course CHEM 0970 taught by Professor Kogut during the Spring '08 term at Pittsburgh.

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Chapter 13 notes - Chapter 13 Objectives (Kinetics) 1. The...

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