Catalysis – homogeneous, heterogeneous and autocatalysis
ChemistryKinetics & EquilibriumAges 15–16Virtual lab
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Use it with your class: students open it from a link or a QR code, with no account needed.
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Five views of how catalysts work: adsorption, bond weakening and desorption on iron (Haber process) and the V₂O₅ redox cycle (Contact process) with catalyst poisoning; Fe²⁺/Fe³⁺ catalysis of S₂O₈²⁻ + 2I⁻; autocatalysis by Mn²⁺ in the MnO₄⁻/C₂O₄²⁻ reaction with its rate–time curve; a bench that decomposes H₂O₂ with Fe³⁺, MnO₂, platinum or catalase and recovers the solid catalyst; and energy profiles of catalysed and uncatalysed routes.
Lesson: Catalysts: homogeneous, heterogeneous and enzyme catalysis, autocatalysis
What it shows
A catalyst speeds up a reaction by providing a different route with a lower activation energy, and it is left chemically unchanged at the end. A heterogeneous catalyst is in a different phase from the reactants: gases adsorb on a solid surface, their bonds weaken, new bonds form and the products desorb; poisons block the active sites. A homogeneous catalyst is in the same phase and often works by changing its oxidation state, as Fe²⁺/Fe³⁺ does. In autocatalysis a product is the catalyst, so the reaction speeds up as it goes. Enzymes such as catalase are biological catalysts.
How to use
In Surface, choose the Catalyst surface, press Run and follow the dashed site through the steps; raise Poisoned sites and compare the rate. In Solution, run with No catalyst, Fe²⁺ and Fe³⁺. In Autocatalysis, run at 60 °C, then tick Add Mn²⁺ at the start. In H₂O₂ bench, choose a Catalyst, run and press Filter, dry and weigh the catalyst. In Energy profiles, choose a Reaction.
Parameters you can change
- View Surface, Solution, Autocatalysis, H₂O₂ bench, Energy profiles
- Catalyst surface Iron (Haber process), V₂O₅ (Contact process)
- Poisoned sites 0–100 %
- Catalyst added (solution) No catalyst, Fe²⁺, Fe³⁺
- Temperature (autocatalysis) 20–80 °C
- Add Mn²⁺ at the start
- Catalyst (H₂O₂ bench) No catalyst, Fe³⁺ solution (homogeneous), MnO₂ powder (heterogeneous), Platinum gauze (heterogeneous), Liver (catalase, enzyme), Potato (catalase, enzyme)
- H₂O₂ concentration 0.1–0.8 mol/dm³
- Boil liver or potato first
- Reaction (energy profiles) Decomposition of H₂O₂, Haber process (iron), Contact process (V₂O₅), S₂O₈²⁻ + I⁻ (Fe²⁺/Fe³⁺)
- Show catalysed route
Questions to explore
- Why does a catalyst not change ΔH or the position of equilibrium?
- Why can either Fe²⁺ or Fe³⁺ catalyse the reaction between S₂O₈²⁻ and I⁻?
- Why does the reaction between MnO₄⁻ and C₂O₄²⁻ start slowly and then speed up?
