Reversible Reaction

In a closed system, reactants can change into products while products change back into reactants. Equilibrium is reached when both directions happen at the same rate, so the amounts stay steady.

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In the picture

The sealed glass vessel holds both red and blue spheres.
The upper tube carries red spheres to the right, one direction of the change.
The lower tube carries blue spheres to the left, the opposite direction.
The level balance shows the two directions proceeding at equal rates.

Examples

A sealed bottle of soda keeps carbon dioxide dissolving into and escaping from the liquid at equal rates.
A saturated salt solution has salt dissolving and crystallizing at the same rate.

Key takeaways

At equilibrium, forward and reverse reactions continue at equal rates.
Equilibrium does not mean equal amounts; it means the concentrations stay steady.