Reaction Rate and Collision Theory Simulator
Equations in this simulation
| [A], [B] | Molecules of A | more molecules in the same box means more collisions per second, so the rate rises with each concentration | |
|---|---|---|---|
| rate | reactions per second | counted in the box, averaged over the last few seconds | |
| k | rate constant | everything about a single collision: how often molecules meet and how many collisions have enough energy |
With the current values:
| Ea | Activation energy Ea (kJ/mol) | the least energy a collision needs, along the line between the two centers, to break the old bonds; real reactions have 40 to 200 kJ/mol, smaller here so you can watch it happen | |
|---|---|---|---|
| R | gas constant | 8.314 J/(mol·K) | |
| T | Temperature T (K) | ||
| fraction | share of collisions with enough energy | the theory, against the share measured in the box |
With the current values:
| A | frequency factor | how often molecules collide in the right orientation; it changes little with temperature | |
|---|---|---|---|
| k ÷ k(300 K) | speed-up compared with room temperature | for Ea = 50 kJ/mol, warming by 10 °C nearly doubles the rate |
With the current values:
| f(E) | Maxwell–Boltzmann distribution of energies | the chart: the area to the right of the red line is the share of molecules with more than Ea; it grows fast as the curve flattens at higher T |
|---|
How to use the reaction rate simulator
- The box holds red molecules of A and blue molecules of B, flying about and bouncing off each other. When an A hits a B hard enough, with more energy along the line between their centers than the activation energy, they react: a flash, and a green molecule of C takes their place.
- Raise the temperature: the molecules speed up, and the share of collisions with enough energy rises far faster than the number of collisions does. Add more A or B and there are more collisions per second. Tick Add a catalyst to lower the barrier and watch the rate jump at the same temperature.
- Compare the share of A–B collisions that reacted, counted in the box, with the e^(−Ea/RT) the theory predicts. The chart shows the Maxwell–Boltzmann distribution of energies, with the activation energy as a red line: the shaded tail beyond it is what reacts.
Frequently asked questions
What is collision theory?
Molecules react only when they collide, with enough energy and the right orientation. The rate is the number of collisions per second times the fraction that succeed. More molecules in the same space mean more collisions; a higher temperature means more collisions and, much more importantly, a larger share with enough energy.
Why does a small rise in temperature speed up a reaction so much?
Because the share of collisions with more than the activation energy is e^(−Ea/RT), which grows steeply with T. For a typical Ea of 50 kJ/mol, going from 25 °C to 35 °C raises that share by about 90%: the rule of thumb that 10 °C doubles a rate. The average energy of the molecules rises by only 3%.
How does a catalyst work?
It gives the reaction another route with a lower activation energy, for example by holding the molecules on a surface in the right position. Many more collisions then get over the barrier at the same temperature. The catalyst is not used up, and it speeds up the forward and reverse reactions alike, so it does not change where an equilibrium lies.
Why are the activation energies here so small?
So that you can watch reactions happen. With a real activation energy of 50 to 100 kJ/mol at room temperature, only one collision in 10⁹ to 10¹⁸ succeeds, and in a box of 160 molecules none would react for longer than you would wait. The simulation uses 2 to 25 kJ/mol; the equations are the same, and the Arrhenius ratio shows what a larger Ea would do.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.