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Interactive Exothermic and Endothermic Energy Diagrams

Run the energy diagram explorer fullscreen
Edit the MicroSim in the p5.js editor

About This MicroSim

The simulator juxtaposes exothermic and endothermic energy profiles on the same canvas. Sliders control the activation energy and enthalpy change, a radio toggle flips between exothermic/endothermic modes, and a catalyst checkbox adds a lowered Ea curve. Numeric readouts summarize Ea and ΔH, and arrows illustrate their physical meaning.

How to Use

  1. Choose Exothermic or Endothermic to set the relative product energy level.
  2. Adjust Activation Energy to raise/lower the transition-state peak. The Ea arrow updates immediately.
  3. Move the ΔH slider to change the energy difference between reactants and products (negative for exothermic, positive for endothermic). The ΔH arrow changes color accordingly.
  4. Check Show catalyst to add a second (green) curve with a smaller Ea but the same ΔH.
  5. Read the numeric Ea and ΔH values in the box at the top-right of the diagram.

Classroom Ideas

  • Compare profiles: Have students capture screenshots for exothermic vs. endothermic settings and label Ea and ΔH.
  • Catalyst discussion: Toggle the catalyst checkbox to emphasize that catalysts lower Ea without changing ΔH.
  • What-if scenarios: Ask learners to predict how rate and heat release change as Ea and ΔH sliders move.
  • Essay prompt: “Why does an exothermic reaction still need activation energy?”—students can explain using the diagram.

Lesson Plan

Grade Level

Grades 10–12 (AP Chemistry Unit 6) and introductory general chemistry

Duration

10-minute lecture demo or guided practice

Prerequisites

  • Understanding of potential energy diagrams
  • Definition of activation energy and enthalpy change
  • Qualitative idea of catalysts

Activities

  1. Live demo (3 min): Teacher toggles between exo/endo and shows how Ea/ΔH arrows shift.
  2. Pair activity (5 min): Students set specific Ea and ΔH values and jot down observations.
  3. Reflection (2 min): Learners write one sentence explaining the catalyst’s effect on Ea vs. ΔH.

Assessment

  • Exit ticket: “Provide Ea/ΔH values for a given slider setting and state whether the reaction is exothermic or endothermic.”
  • Homework extension: Students annotate a screenshot with the definitions of Ea, ΔH, and transition state.

References

  1. Brown, LeMay, Bursten, Murphy. Chemistry: The Central Science, 15th ed., Pearson, 2022 — Enthalpy diagrams and activation energy.
  2. House, J. E. Principles of Chemical Kinetics, 3rd ed., Academic Press, 2015 — Catalysis and energy barriers.