# Reaction kinetics (AS)

> CIE A-Level Chemistry · CIE 9701 AS
> Source: https://www.owlsprep.com/study/cie-9701-u8-overview/
> Weight: n/a

This unit introduces core concepts of reaction kinetics, the study of how fast chemical reactions proceed and what factors alter their rate. These concepts underpin all industrial chemistry and biological reaction systems.

**Prerequisites:** [Basic knowledge of chemical energetics and bonding](https://www.owlsprep.com/study/cie-9701-u5-energetics-overview/)

## Learning objectives

- Define reaction rate and calculate rate from experimental concentration data
- Explain how temperature, concentration, and surface area affect rate using collision theory
- Describe how catalysts work in terms of activation energy and reaction pathways
- Classify catalysts as homogeneous or heterogeneous for common reactions

## Unit at a glance

The topics in this unit build logically from foundational measurement to explanatory models and real-world application. We start with how to measure and calculate reaction rate, then use collision theory to explain why different factors change reaction speed, before finally applying this model to understand how catalysts work.

Explore the 3 interconnected sub-topics below:
- [Rates of reaction](https://www.owlsprep.com/study/cie-9701-u8-rates-of-reaction/) — Learn how to define, measure, and calculate reaction rate from experimental data.
- [Collision theory](https://www.owlsprep.com/study/cie-9701-u8-collision-theory/) — Use the collision theory model to explain how common factors alter reaction rate.
- [Catalysis](https://www.owlsprep.com/study/cie-9701-u8-catalysis/) — Explore how catalysts lower activation energy and classify homogeneous/heterogeneous catalysis.

## Common pitfalls

- **Wrong:** Confusing reaction rate with reaction extent/yield
  - Why it fails: Rate measures how quickly a reaction proceeds, not how much product forms when it finishes.
  - Correct: Remember a fast reaction can have low yield, and a slow reaction can go to completion.
- **Wrong:** Forgetting that catalysts are chemically unchanged at the end of a reaction
  - Why it fails: Catalysts take part in the reaction but are regenerated, so they do not get used up.
  - Correct: Always recall catalysts are regenerated, only change the reaction pathway, not the overall enthalpy change.

## Cheatsheet

| Concept | Key Definition/Fact |
| --- | --- |
| Rate of reaction | Change in concentration of reactant/product per unit time: $rate = \frac{\Delta [X]}{\Delta t}$ |
| Activation energy ($E_a$) | Minimum energy colliding particles must have to undergo a successful reaction |
| Effect of temperature increase | Increases the proportion of particles with energy ≥ $E_a$, raising the frequency of successful collisions |
| Homogeneous catalyst | Catalyst that is in the same physical state as the reactants |
| Heterogeneous catalyst | Catalyst that is in a different physical state to the reactants |

## What's next

Begin your study of this unit with the first sub-topic, which covers the core definitions and calculations you will need for all subsequent kinetics work. After you complete all sub-topics in this unit, move on to the next unit on chemical equilibrium, which explores how far reactions proceed, complementing what you learned about how fast they go here.

- [Rates of reaction](https://www.owlsprep.com/study/cie-9701-u8-rates-of-reaction/)
- [Collision Theory](https://www.owlsprep.com/study/cie-9701-u8-collision-theory/)
- [Catalysis](https://www.owlsprep.com/study/cie-9701-u8-catalysis/)

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