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Surface area and particle size effects

The rate and extent of chemical change • Rate of reaction

Key concepts

What you'll likely be quizzed about

  • Surface area is the total area of a solid's outer surfaces.
  • Particle size refers to the dimensions of individual pieces of a solid, from large lumps to fine powders.
  • Smaller particles create a larger surface area for a given mass than larger particles, resulting in increased collision opportunities between reactants.

Flashcards

Test your knowledge with interactive flashcards

Predict the rate change when a metal lump is crushed into powder, keeping mass constant.

Click to reveal answer

Crushing a lump into powder increases surface area and SA:V, leading to an increased reaction rate under the same conditions.

Key notes

Important points to keep in mind

Surface area increases collision frequency; activation energy remains unchanged.

SA:V increases as particle size decreases; for cubes SA:V = 6/s, for spheres SA:V = 3/r.

Smaller pieces of the same mass react faster due to increased total exposed area.

Surface area influences reaction rate only when it is the limiting factor.

Maintain constant temperature, concentration, and mixing when testing surface area effects.

Agglomeration, coatings, or poor mixing can limit effective surface area.

Predict changes by evaluating SA:V before and after size changes.

Report observations like gas volume, color change, or temperature change to indicate rate differences.

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