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Kinetic Time Scales

Kinetic Time Scales. Light absorption. Explosions. Corrosion. Geological. Energy Barrier in Reactions. Chemical and physical reactions have energy barriers, or an activation energy ( E a ), that must be overcome to permit reaction

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Kinetic Time Scales

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  1. Kinetic Time Scales Light absorption Explosions Corrosion Geological

  2. Energy Barrier in Reactions • Chemical and physical reactions have energy barriers, or an activation energy (Ea), that must be overcome to permit reaction • Unassisted reaction  Diet Coke bottle left open for several days • Catalysts act to lower this energy barrier and enhance speed • Mentos (and other additives) can be considered catalysts for the physical reaction in which dissolved CO2 changes to gaseous CO2 • Catalyzed reaction much faster than unassisted reaction (control)

  3. Mentos as a Catalyst http://www.stevespanglerscience.com/experiment/original-mentos-diet-coke-geyser

  4. Mentos as a Catalyst • Contributing factors • Rough surfaces • Promotes nucleation, or formation, of CO2 bubbles from dissolved CO2 • Rapid descent of “catalyst” particles • Low friction from surfactants and shape • Relatively heavy • Rapid reaction in large bottles Scanning Electron Microscope (SEM) image of Mentos candy surface Scale bar is 20 μm long (20 millionths of a meter) Coffey, T. S., Am. J. Phys. 2008, 76, 551.

  5. Table Salt as a Catalyst • Contributing factors • Rough surfaces • Slower descent into bottle • Smaller particles • Slower reaction in larger bottle • High surface area-to-volume ratio • Along with surface roughness, promotes rapid reaction in smaller scale systems (indoor experiments) SEM images of table salt Scale bars are (a) 2.0 mm; (b) 100 µm; (c) 50 µm; and (d) 20 μm long Coffey, T. S., Am. J. Phys. 2008, 76, 551.

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