Structure of the Atom
23. Reaction Rates
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Session Overview
| Modules | Reactions and Kinetics |
| Concepts | chemical kinetics: the rate equation, order of reaction, and rate laws for zeroth, first, and second order reactions, temperature dependence of rate of reaction, catalysts, Fick's first law and steady-state diffusion |
| Keywords | steric hindrance, cisplatin, first-order, second-order, zero-order, half-life, radioactive decay, reaction rate, chemical kinetics, rate of reaction, products, reactants, rate constant, rate equation, activation energy, Arrhenius equation, activated complex, decomposition reaction, nuclear decay, linearizing function, least-squares fitting, integral method, differential method, catalysis, reaction coordinate diagram, adsorb, desorb, selectivity, catalyst, inhibitor, diffusion, mass transport, mass flow rate, flux, Fick's first law, concentration gradient, diffusivity, concentration profile, oxidation, reduction |
| Chemical Substances | dinitrogen pentoxide (N2O5), nitrogen dioxide (NO2), oxygen gas (O2), nitric oxide (NO), cisplatin (PtCl2(NH3)2), water (H2O), chloride (Cl-), uranium-238 (238U), thorium-234 (234Th), helium (4He), carbon monoxide (CO), carbon dioxide (CO2), carbon (C), silicon (Si), boron (B), diborane (B2H6), hydrogen gas (H2), octane (C8H18), platinum (Pt), palladium (Pd), rhodium (Rh) |
| Applications | cisplatin, radiocarbon dating, automobile catalytic converter, semiconductor wafer doping (Pentium), Hindenburg fire, corrosion prevention in automobile engines |
Prerequisites
Before starting this session, you should be familiar with:
- Session 22: Introduction to Kinetics (second part)
- Derivative and integral notation, logarithms, fitting a curve to data
- Doping of semiconductors and thermal excitation (Session 14)
Learning Objectives
After completing this session, you should be able to:
- Compare the nature of reactions with first-order and second-order rates.
- Given a set of data about a reaction, calculate the reaction rate, activation energy, reaction order, and/or rate constant, and derive a general expression for the concentration over time.
- Sketch an energy-level diagram for a reaction, labeling key features.
- Describe the properties and behavior of an effective catalyst.
- Calculate the concentration profile in a doped semiconductor wafer using Fick's first law.
Reading
Archived Lecture Notes #8 (PDF), Sections 4-7
Archived Lecture Notes #9 (PDF), Section 1
| Book Chapters | Topics |
|---|---|
 [A&E] 10.7, "The Kinetic Molecular Theory of Gases." | Molecular description of gases; Boltzmann distributions; the relationships between pressure, volume, and temperature; diffusion and effusion; rates of diffusion or effusion |
| [A&E] 14.1, "Factors That Affect Reaction Rates." | Concentration effects; temperature effects; phase and surface area effects; solvent effects; catalyst effects |
| [A&E] 14.2, "Reaction Rates and Rate Laws." | Reaction rates; rate laws |
| [A&E] 14.3, "Methods of Determining Reaction Orders." | Zeroth-order reactions; first-order reactions; second-order reactions; determining the rate law of a reaction |
| [A&E] 14.4, "Using Graphs to Determine Rate Laws, Rate Constants, and Reaction Orders." | Graphing reaction concentration data to show reaction orders and rate constants; typical graphs for zeroth-, first-, and second-order reactions |
| [JS] 5.1, "Thermally Activated Processes." | Arrhenius equation; activation energy; Maxwell-Boltzmann distribution; process mechanisms and rate-limiting steps |
| [JS] 5.2, "Thermal Production of Point Defects." | Activation energy of vacancies vs. interstitials; Arrhenius plot; thermal expansion |
Lecture Video
Download this video:
» iTunes U (MP4 - 225MB)
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Resources
Lecture Summary
First-order chemical reactions (e.g. decomposition of cisplatin, N2O5; radioisotope decay) have concentration-independent rates, which is sometimes expressed as the half-life. Second-order rates (e.g. decomposition of NO2) are inversely proportional to concentration. To determine the order and rate constant of an unknown system, integral and differential methods can be used to linearize experimental data measuring concentration over time. Catalysts affect reaction rates by adsorbing, aligning, or otherwise physically manipulating reactants, changing the activation energy of a reaction. Reaction rates are also limited by mass transport of reactants and products. In solids, atoms move via diffusion, driven by concentration gradients, as described by Fick's first law; the proportionality constant in this case is D, the diffusivity.
Homework
For Further Study
Textbook Study Materials
See the [A&E] companion website for PowerPoint outlines of each chapter, plus online quizzes, interactive graphs and 3D molecular animations:
Supplemental Readings
Fick, Adolf. "Ueber Diffusion." Annalen der Physik 170 (1855): 59-86.
People
Culture
Lauper, Cyndi, and Rob Hyman. "Time after Time." She's So Unusual. Performed by Cyndi Lauper. Epic Records, 1984.
Lennon, John, and Paul McCartney. "Baby You Can Drive my Car." Rubber Soul. Performed by The Beatles. EMI, 1965.
Other OCW and OER Content
| Content | Provider | Level | Notes |
|---|---|---|---|
| 5.60 Thermodynamics and Kinetics | MIT OpenCourseWare | Undergraduate (elective) | Lecture 30: Introduction to Reaction Kinetics |
| Diffusion | DoITPoMS | Undergraduate | |
| Diffusion | Connexions | Undergraduate |
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