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Activation Energy and Catalysts

High schoolChemistryArrhenius first-order conversion with schematic catalyzed and uncatalyzed energy profiles

Click or drag the energy plot to move the reaction-coordinate probe. Add a catalyst, run equal time exposures and compare conversion without moving the reactant and product energies.

Reaction energy landscape

Uncatalyzed pathCatalyzed path
68340-34-6800.250.50.751Reaction coordinateRelative energy (kJ/mol)

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Measurement notebook

Change the setup, test a prediction and save the result. Up to 12 snapshots are kept.

About this experiment

Probe reaction-coordinate energy profiles and compare equal-time conversions. Lower a barrier with a catalyst, vary temperature and see which quantities change while reaction enthalpy stays fixed.

Learning goals

  • Distinguish activation energy from reaction enthalpy.
  • Use Arrhenius temperature dependence to compare rate constants.
  • Explain why a catalyst changes both directional barriers without changing endpoint energies.

How to use it

  1. 1Click the energy profile to read the reactant, transition-state and product energies.
  2. 2Run an uncatalyzed exposure and save its conversion and rate constant.
  3. 3Add the catalyst and repeat the same exposure.
  4. 4Change reaction enthalpy independently and compare the forward and reverse barriers.

The model

Temperature and activation energy set the first-order rate constant.
The barrier difference is the reaction enthalpy.
The half-life applies to the chosen first-order model.

Assumptions

  • The smooth energy profiles are schematic reaction-coordinate diagrams rather than molecular potential calculations.
  • The prefactor is fixed at one million per second. The time trace is an irreversible first-order disappearance law.
  • The Arrhenius exponential is not a measured fraction of all molecular collisions. Orientation and detailed energy distributions are not resolved.
  • A catalyst lowers the forward and reverse barriers by the same selected amount. It does not move either endpoint or calculate a new equilibrium yield.

Try this in class

  1. Q1Why can a small barrier reduction cause a large rate increase?
  2. Q2Why does a catalyst not change the reactant-to-product energy difference?

Frequently asked questions

Is the moving energy probe a reacting molecule?

No. It samples a schematic reaction coordinate independently of the physical exposure clock.

Can this irreversible trace predict equilibrium composition?

No. It isolates first-order conversion and the Arrhenius rate comparison. Equilibrium needs a reversible model.