Session Overview
| Modules | Amorphous Materials, Reactions and Kinetics |
| Concepts |
Amorphous Materialsengineering glasses: network formers, network modifiers, and intermediates, properties of silicate glasses Reactions and Kineticsintroduction to kinetics: activation energy, the rate equation, and the Arrhenius equation, radiocarbon dating |
| Keywords |
Amorphous Materialsthermal shock, glass, silicate glass, network former, network modifier, solidification, molar volume, coefficient of thermal expansion, melting point, glass transition temperature, quenching, excess volume, processing temperature, fluidity, bridging oxygen, terminal oxygen, index of refraction, atomic mobility, rate of cooling, viscosity, lehr, network connectivity, annealing, strain, tempering, free volume, ion exchange, toughness, hardness Reactions and Kineticslaw of mass action, chemical kinetics, rate of conversion, species concentration, rate of reaction, products, reactants, conservation of mass, kinetic theory, order of reaction, rate constant, rate equation, activation energy, Arrhenius equation, activated complex, Maxwell-Boltzmann, reaction coordinate diagram, radiocarbon dating, Shroud of Turin, radioactive decay, half-life, barrier energy, reaction mechanism, thermal promotion |
| Chemical Substances |
Amorphous Materialssilicate glass (SiO2), sodium oxide (Na2O), calcium oxide (CaO), magnesium oxide (MgO), borate glass (B2O3), aluminum oxide (Al2O3), potassium oxide (K2O), potassium chloride (KCl) Reactions and Kineticssodium azide (NaN3), nitrogen gas (N2), sodium (Na), potassium nitrate (KNO3), carbon monoxide (CO), chlorine gas (Cl2), phosgene gas (COCl2) |
| Applications |
Amorphous Materialsautomobile windshields, Pyrex, lead crystal, windows, glass cookware and labware, case-hardened/carburized/tool steel Reactions and Kineticsautomobile airbags, phosgene gas, radiocarbon dating |
Prerequisites
Before starting this session, you should be familiar with:
- Properties, composition, and manufacturing of glass (Session 21)
- The shapes of molecules and factors affecting their mobility (Session 8 through Session 12)
- How to write chemical equations (Session 2)
- The distribution of energies per the Maxwell-Boltzmann curve (Session 14)
Looking Ahead
The solution hardening processes (chemically toughened glass, carburized steel) described in this session involve diffusion along concentration gradients, as quantified in Session 23 and Session 24.
Learning Objectives
After completing this session, you should be able to:
- Describe how to design glasses with the following properties: thermal shock resistance; low working temperature; high yield stress; high index of refraction; high optical clarity.
- Explain how intermediates act as network formers in some mixes and modifiers in others.
- Contrast thermal strengthening of glass with chemical strengthening.
- Write the rate law for a given chemical reaction, and determine the values of the rate constant k, rate order n, and activation energy Ea from the available data.
- Explain the effect of temperature on chemical reactions using the Maxwell-Boltzmann distribution.
- For a multi-step reaction, determine which step is rate-limiting and write the overall rate law.
- Describe how radioisotope dating works, and calculate the age of artifacts using their 14C content.
Reading
Archived Lecture Notes #7 (PDF)
Archived Lecture Notes #8 (PDF)
| Book Chapters | Topics |
|---|---|
| [Saylor] 14.5, “Half-Lives and Radioactive Decay Kinetics.” | Half-lives, radioactive decay rates, radioisotope dating techniques |
| [Saylor] 14.6, “Reaction Rates – A Microscopic View.” | Molecularity and the rate-determining step, chain reactions |
| [Saylor] 14.7, “The Collision Model of Chemical Kinetics.” | Activation energy, graphing the energy changes during a reaction, the Arrhenius equation |
| [JS] 12.2, “Glasses – Noncrystalline Materials.” | Network formers, modifiers, and intermediates; commercial silicate glasses; nonsilicate glasses; applications of amorphous solids |
| [JS] 12.3, “Glass-Ceramics.” | Heat treatment and crystallization, mechanical and thermal shock resistance, nucleating agents, glass processing techniques |
Lecture Video
Resources
Lecture Summary
Glasses can be engineered for specific applications by altering their proportions of network formers, network modifiers, and intermediates (e.g. Al2O3), and through careful processing. For example, glass can be strengthened by introducing compressive stress near the surface, by thermal (e.g. tempering) or chemical treatment (e.g. solution hardening).
The next unit covers chemical kinetics, the study of reaction rates and mechanisms. For a generalized reaction system, the rate of change of ci (concentration of species i) is proportional to the instantaneous concentration of ci; the exact values of the rate constant k and the rate order n are typically determined by experiment. The rate constant can be increased by raising the temperature and/or lowering the activation energy. Radiocarbon dating, although not a chemical reaction, has a first-order rate law, resulting in a constant decay rate over time.
Homework
Textbook Problems
| [saylor] Sections | Conceptual | Numerical | Application |
|---|---|---|---|
| [Saylor] 14.2, “Reaction Rates and Rate Laws.” | none | 5, 6 | none |
| [Saylor] 14.6, “Reaction Rates – A Microscopic View.” | 4 | 3 | none |
| [Saylor] 14.7, “The Collision Model of Chemical Kinetics.” | 1 | 1, 4, 5 | none |
| [Saylor] 14.9, “End-of-Chapter Material.” | none | none | 5 |
For Further Study
Supplemental Readings
Libby, Willard F. Radiocarbon Dating. Chicago, IL: University of Chicago Press, 1969.
People
Svante Arrhenius – 1903 Nobel Prize in Chemistry
Willard Libby – 1960 Nobel Prize in Chemistry
Culture
Chambers, Joe, and Willie Chambers. “Time Has Come Today.” The Time Has Come. Performed by The Chambers Brothers. Columbia Records, 1967.
Other OCW and OER Content
| Content | Provider | Level | Notes |
|---|---|---|---|
| Fracture of Glass | DoITPoMS | Undergraduate | |
| 5.60 Thermodynamics and Kinetics | MIT OpenCourseWare | Undergraduate (elective) | Lecture 30: Introduction to Reaction Kinetics |
