Chemistry · Kinetics

Reaction Rates and Activation Energy Explorer

Set the temperature and the activation energy for a first-order reaction, with or without a catalyst. The energy distribution graph shows which molecules have enough energy to react.

Watch the rate constant, the half-life, and the concentration curve change. The Arrhenius graph shows why a small temperature change can change the rate a lot.

Model notes

Arrhenius equation: k = A e^(−Ea/RT), with R = 8.314 J/(mol·K). The pre-exponential factor A is fixed at 1.0 × 10¹⁰ s⁻¹, a typical order of magnitude for a unimolecular reaction in a classroom model. Real reactions have their own measured A.
The reaction is first order: [A] = [A]₀ e^(−kt), half-life t½ = ln 2 ÷ k. The starting concentration is 1.00 M.
The energy graph uses a log scale so that the tail is visible. The shaded fraction of molecules uses the Maxwell-Boltzmann energy distribution for translational energy in three dimensions, F(E > Ea) = erfc(√x) + 2√(x/π) e^(−x), with x = Ea/RT. The Arrhenius k uses the simpler factor e^(−Ea/RT). The two are close when Ea is much larger than RT.
The catalyst is modeled as lowering Ea by 20 kJ/mol and leaving A unchanged. Real catalysts change the reaction pathway, and the size of the change depends on the catalyst.
The reference line on the concentration graph is the setting 298 K, Ea 70 kJ/mol, no catalyst.

Sources

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