Set the barrier and the temperature, then watch the reaction run.
Reaction Rate simulator
This simulation needs a modern browser with canvas support. The measurements and formula below still describe the physics.
Live measurements
Controls
Graph
Formula
log₁₀ k = log₁₀ A − Ea / (2.303 × R × T)
- log₁₀ k Rate constant, log₁₀
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Observations
What's happening
Real-world examples
Runs in seconds
A 60 kJ/mol barrier at room temperature with a typical pre-exponential factor gives a half-life of about a quarter of a second. The flask empties while you watch.
Too slow to see
Raise the barrier to 120 kJ/mol and nothing appears to happen. The half-life is now measured in thousands of years, which is the honest answer rather than a bug.
Same reaction, heated
Take that 120 kJ/mol reaction to 500 K and it finishes in seconds. Nothing about the molecules changed; only the fraction of collisions with enough energy did.
Second order tail
Switch to second order and the curve drags. Each half-life is twice as long as the one before, so the last few percent takes longer than everything else put together.
Uses of reaction rate
- Estimating the shelf life of a drug from an accelerated stability test
- Choosing a reaction temperature that finishes in a working day
- Explaining why food keeps longer in a fridge than on a counter
reaction rate pitfalls
- Assuming every reaction has a concentration-independent half-life
- Confusing the rate with the rate constant
- Using degrees Celsius instead of kelvin in the Arrhenius equation
reaction rate questions (8)
What is the Arrhenius equation?
The Arrhenius equation gives the rate constant from temperature: k = A x e^(-Ea / RT). A is the pre-exponential factor, which counts how frequently molecules collide with the right geometry. The exponential term is the fraction of those collisions carrying enough energy to clear the barrier. Because Ea sits in the exponent, a small change in it moves k enormously.
What is activation energy?
Activation energy is the energy barrier between reactants and products, measured at the transition state. It is the peak on the reaction coordinate drawn here. Reactants that cannot reach the peak fall back, so the barrier height decides how many collisions succeed. It says nothing about whether the reaction releases energy overall.
How do you calculate the half-life of a reaction?
It depends on the order. First order gives t = ln 2 / k, which ignores concentration. Zero order gives t = [A]0 / 2k, so it shortens as reactant runs out. Second order gives t = 1 / (k [A]0), so it lengthens. Switch orders on the slider and the half-life readout jumps, even though k has not moved.
What is the difference between zero, first and second order reactions?
The order says how the rate responds to concentration. Zero order ignores it, so [A] falls in a straight line and hits zero. First order is proportional to [A], giving the exponential decay everyone recognises. Second order goes with [A] squared, so the curve drops fast then drags. Plotted against half-lives, those three shapes are the whole difference.
Why does a 10 degree temperature rise double the rate?
It is arithmetic rather than a law. For an activation energy near 50 kJ/mol at room temperature, the exponential term changes by roughly a factor of two over ten kelvin. Change the activation energy and the factor changes with it, which the rate change readout shows live. Treat the doubling rule as a rough guide for typical barriers.
What is the difference between rate and rate constant?
The rate is how fast concentration is changing right now, and it falls as the reactant is used up. The rate constant k does not change during a run at fixed temperature. This is a common mistake in exam answers: a first order reaction slows down while its rate constant stays exactly where it started.
Does a catalyst change how far a reaction goes?
No. A catalyst lowers the activation energy, so the reaction reaches its destination sooner. It leaves the energies of the reactants and products alone, so the equilibrium position is unchanged. Drop the activation energy slider and watch the half-life collapse while the final conversion stays exactly where it was.
Why do the readouts show logarithms instead of the numbers themselves?
Because the numbers span forty orders of magnitude. Across the slider ranges here, k runs from about 10^-38 to 10^15, and no fixed decimal readout stays useful over that. Logarithms keep every setting readable, and they are the same axis an Arrhenius plot uses, so the readout matches how the data gets plotted anyway.