Reaction Rate Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Reaction Rate.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

The speed at which reactants are converted into products in a chemical reaction, quantified as the change in concentration of a reactant or product per unit time.

How quickly the reaction happens—from instant explosion to years of rusting.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Rate depends on concentration, temperature, surface area, and catalysts.

Common stuck point: Doubling concentration doesn't always double rate—depends on the reaction mechanism.

Sense of Study hint: When calculating reaction rate, use the change in concentration over change in time. First identify whether you are tracking a reactant (decreasing) or product (increasing). Then apply \text{rate} = -\frac{\Delta[\text{reactant}]}{\Delta t} or \frac{\Delta[\text{product}]}{\Delta t}. Finally, account for stoichiometric coefficients when comparing rates of different species.

Worked Examples

Example 1

easy
List four factors that affect the rate of a chemical reaction and explain how each works.

Solution

  1. 1
    Temperature: higher temperature → faster molecular motion → more frequent and energetic collisions → faster rate.
  2. 2
    Concentration: higher concentration → more reactant particles per volume → more frequent collisions → faster rate.
  3. 3
    Surface area: finer particles → more exposed surface → more collisions per unit time → faster rate.
  4. 4
    Catalyst: lowers activation energy → greater fraction of successful collisions → faster rate.

Answer

\text{Temperature, concentration, surface area, catalyst}
All four factors relate to collision theory: reactions occur when particles collide with sufficient energy and proper orientation. Anything that increases effective collisions increases the rate.

Example 2

medium
In a reaction, the concentration of a reactant decreases from 0.80\,\text{M} to 0.20\,\text{M} over 120 seconds. Calculate the average rate of reaction.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Why does increasing temperature speed up a chemical reaction?

Example 2

medium
Two equal masses of calcium carbonate react with the same acid. One sample is powder and the other is large chips. Which reacts faster, and why?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

chemical reaction