The line is the energy. A ball’s height is its energy, so to cross the barrier it needs enough energy to rise above the top. Drag the three handles on the line, or use the sliders.
Molecules vs time
Q approaching K
How it works: balls move under gravity over a hard surface shaped like the energy curve, so a ball’s height is its potential energy. Balls bump into each other and into an invisible background gas that keeps them at the temperature you set. A ball counts as R left of the barrier top and as P right of it.
At equilibrium the balls spread out as they would in a gravitational field, which gives K = [P]/[R] ≈ e−ΔE/RT for two plateaus of equal width. ΔE, the level of P minus the level of R, plays the role of ΔG° in the slides. The barrier changes how fast equilibrium is reached, not where it ends up.
Inspired by the PhET “Reversible Reactions” simulation (University of Colorado Boulder). This is an independent re-implementation, not a copy of it.