What is a reaction rate?

A reaction rate is a measure of how fast a reactant disappears or a product forms during a reaction.

Explanation:

It is usually defined as the change in concentration per unit time:

Δ (concentration) / Δt

The units are (moles per litre) per second.

In symbols, the units are mol / (L·s) or mol·L^-1 s^-1.