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Catalyzed vs. Uncatalyzed Energy Profile

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About This MicroSim

The simulation plots both the uncatalyzed and catalyzed potential-energy curves on the same diagram. A catalyst-strength slider lowers the catalyzed activation barrier, an exothermic/endothermic toggle flips ΔH, an intermediate checkbox adds a two-step catalyzed pathway, and a radio selector chooses which curve a reaction “ball” rolls along. Activation-energy arrows and tooltips help students read numerical Ea and ΔH values.

How to Use

  1. Drag Catalyst Strength to reduce the catalyzed barrier and see how Ea₍cat₎ changes relative to Ea₍uncat₎ while ΔH stays fixed.
  2. Use Reaction Profile (Exothermic or Endothermic) to raise/lower the product energy level and observe how both curves shift. ΔH arrow updates automatically.
  3. Check Show Intermediate to display a two-peak catalyzed pathway (multi-step mechanism). Uncheck to return to a single peak.
  4. Select Animate Path (Uncatalyzed or Catalyzed) to watch a marker roll over the chosen curve, illustrating barrier crossing.
  5. Hover over labeled points to read energy values (reactants, products, transition states).

Classroom Ideas

  • Ea comparison: Have students record both Ea values for several catalyst strengths and relate them to qualitative rate discussions.
  • Mechanism visualization: Enable the intermediate and ask learners to describe how catalysts introduce additional steps with lower individual barriers.
  • Thermodynamics vs kinetics: Toggle between exothermic/endothermic to reinforce that catalysts change Ea but not ΔH.
  • Speaking prompt: Students narrate what happens to the reaction ball when the catalyzed barrier drops—linking energy diagrams to collision theory.

Lesson Plan

Grade Level

Grades 11–12 (AP Chemistry Unit 5) and college introductory kinetics

Duration

10–15 minutes as a lecture demo or guided practice activity

Prerequisites

  • Understanding of activation energy and ΔH
  • Familiarity with catalysts and their effect on rate vs enthalpy
  • Ability to interpret basic potential-energy diagrams

Activities

  1. Demo (3 min): Teacher toggles exothermic/endothermic and catalyst strength to show how Ea changes while ΔH stays constant.
  2. Guided inquiry (7 min): Students work in pairs to fill out a table of Ea₍uncat₎, Ea₍cat₎, and ΔH for three catalyst strengths and both thermal profiles.
  3. Reflection (3 min): Learners explain why a two-step catalyzed mechanism can have smaller individual barriers yet the same overall ΔH.

Assessment

  • Exit ticket: “If a catalyst halves Ea but leaves ΔH unchanged, what happens to the reaction rate and why?”
  • Screenshot submission: Students capture the diagram with the intermediate shown and annotate where Ea and ΔH are read.

References

  1. House, J. E. Principles of Chemical Kinetics, 3rd ed., Academic Press, 2015 — Catalysis and energy profiles.
  2. Atkins & de Paula. Physical Chemistry, 11th ed., Oxford University Press, 2017 — Activation energy, catalysis, and mechanism diagrams.