The lab draws the energy profile of a single-barrier reaction. You choose the forward barrier, the reaction enthalpy and the temperature, optionally add a catalyst, and move a marker along the reaction coordinate. The rate constant follows the Arrhenius equation.
• A reactant energy shelf, two activation pathways, a product energy shelf, a reaction-coordinate marker and a thermal activation display. • Sliders for the uncatalyzed forward barrier (50 to 120 kJ/mol), reaction enthalpy ΔH (−40 to 40 kJ/mol), temperature (250 to 600 K) and reaction coordinate (0 to 1), with toggles for the catalyst, coordinate animation and explanatory particles. • Readouts: active forward barrier, active reverse barrier, reaction enthalpy, k relative to the uncatalyzed k at the same temperature, the illustrative rate constant and the coordinate. • Experiments: a catalyst lowers the barrier and raises k while ΔH stays at −30 kJ/mol; an endothermic path ends with products above reactants.
k = A exp(−E_a/RT) with A = 10¹² s⁻¹. The reverse barrier is E_a,reverse = E_a,forward − ΔH. The catalyst model is E_a,cat = max(ΔH + 5, 0.6 E_a) kJ/mol. A catalyst changes barriers but not ΔH or the equilibrium position.
Profiles are illustrative single-barrier energy diagrams with an assumed Arrhenius prefactor. Coordinate playback is not reaction-time integration or a mechanism. The catalyst changes barriers, not ΔH or equilibrium, and the reverse barrier stays positive across the control ranges.
It lowers the activation barrier, speeding both directions, but it does not change the reaction enthalpy or the equilibrium. The lab shows ΔH unchanged while k rises.
In the Arrhenius expression exp(−E_a/RT) grows quickly with T, so a larger fraction of molecular encounters can cross the barrier.
E_a,reverse = E_a,forward − ΔH. An endothermic step (ΔH > 0) has a forward barrier larger than the reverse barrier.
No. It uses a fixed prefactor of 10¹² s⁻¹ and is labeled illustrative. Use it to compare trends, not to predict real kinetics.