Reaction Mechanism & Rate-Determining Step
See a two-step mechanism as an energy profile, drag the peaks and find the slowest step and rate law.
Choose a mechanism, then drag the orange peaks. The taller barrier is the slow (rate-determining) step.
About the Reaction Mechanism & Rate-Determining Step
Free reaction mechanism & rate-determining step. See a two-step mechanism as an energy profile, drag the peaks and find the slowest step and rate law. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for reactions & kinetics, the reaction mechanism & rate-determining step runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
See a two-step mechanism as an energy profile, drag the peaks and find the slowest step and rate law. Use it to explore reactions & kinetics ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Reaction Mechanism & Rate-Determining Step
- Use the controls to change Mechanism. The simulation reacts instantly.
- Pick an option such as SN1 (2 steps), NO₂ + CO, Ozone + Cl catalyst, Custom to switch modes or load an example.
- Press "Play reaction" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Drag TS₁ above TS₂, then the reverse, and watch the slow step change.
- Play the ball through the SN1 mechanism.
- Read the rate law of each mechanism.
Key ideas you can learn
- Many reactions happen in several elementary steps.
- The step with the biggest barrier is the rate-determining step.
- The rate law comes from the slow step.
- Intermediates are made in one step and used in the next.
Where this is used in the real world
Chemists study mechanisms to design faster catalysts, make drugs more efficiently and understand ozone depletion.
Who is this simulation for?
Students learning reaction rates, equilibrium and equations, and teachers who want a visual way to explain what happens to particles.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
What is the rate-determining step?
The slowest elementary step. It limits how fast the overall reaction can go.
What is the difference between an intermediate and a transition state?
An intermediate is a real species in an energy valley; a transition state is the unstable peak between species.
Is the Reaction Mechanism & Rate-Determining Step free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Reaction Mechanism & Rate-Determining Step work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.