How is the rate of a chemical reaction defined?

The rate of a chemical reaction tells us how fast a reaction happens—that is, how quickly reactants are used up or products are formed.

Simple Definition:

• Reaction rate = Change in concentration of a substance ÷ Time

Explanation in simple terms:

1. If a substance disappears, its concentration decreases over time.
2. If a substance forms, its concentration increases over time.
3. The faster the change, the faster the reaction.

Example:

• If 2 moles of a gas are produced in 4 seconds, the rate = 2 ÷ 4 = 0.5 moles/second.

Key idea:

• Reaction rate tells us “how fast the reaction is going”, usually measured in moles per liter per second (mol/L·s).