---
title: "Rates of Reaction: Collision Theory and What Changes a Rate"
description: "A reaction happens when particles collide often enough and hard enough. Concentration, surface area, temperature, pressure and catalysts each change one of those two things, and a rate is read as the "
canonical: https://lightmysky.com/learn/science/rates-of-reaction-collision-theory-and-what-changes-a-rate-mt_Ma2bOotr9g
source: https://lightmysky.com/learn/science/rates-of-reaction-collision-theory-and-what-changes-a-rate-mt_Ma2bOotr9g.md
retrieved: 2026-09-12
---

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# Rates of Reaction: Collision Theory and What Changes a Rate

A reaction happens when particles collide often enough and hard enough. Concentration, surface area, temperature, pressure and catalysts each change one of those two things, and a rate is read as the gradient of a graph.

Subject: Science · Area: Matter & Materials · Ages 15 to 16
Page: https://lightmysky.com/learn/science/rates-of-reaction-collision-theory-and-what-changes-a-rate-mt_Ma2bOotr9g

## Ready when they can

- Explains each factor in terms of how often particles collide or how much energy they bring
- Works out a mean rate from a mass loss or gas volume graph, and says why the curve flattens
- Explains how a catalyst speeds a reaction up without being used up, using the activation energy
- Decides which of two curves on the same axes belongs to the faster run and justifies it

## Lesson: Crashes, dials and curve reading

A reaction happens when particles collide with enough energy and the right facing. Most bumps fail one of those tests. The rate is really the count of successful crashes each second. Anything that raises that count speeds the reaction up.

Five dials tune the count. Higher concentration or gas pressure crowds particles, so meetings grow more frequent. Higher temperature gives more collisions enough energy and raises meeting rates. Powders beat lumps because more surface lies exposed, as marble chips in acid show. A catalyst opens an easier path with lower activation energy, and it is not used up.

**Example.** Read rates off a graph of gas volume or mass loss against time. The mean rate is amount divided by time. If 60 cm3 forms in the first 30 s, the mean rate is 60 divided by 30, which is 2 cm3/s. Curves start steep and flatten as reactants drain away.

**Tip.** Compare runs on the same axes. The steeper starter is the faster run. If both curves level at the same total, the speed differed but the final amount did not. A catalyst does exactly this: quicker arrival, same harvest.

**Recap.** Collisions drive rates, five dials tune them, and graph slopes reveal the speed.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Reaction Profiles and Activation Energy](https://lightmysky.com/learn/science/reaction-profiles-and-activation-energy-mt_6LtFkXn_xQ)
- [Pollutants from Burning Fuels](https://lightmysky.com/learn/science/pollutants-from-burning-fuels-mt_DDiyDBy6YW)
- [Concentration of Solutions in Moles per Cubic Decimetre](https://lightmysky.com/learn/science/concentration-of-solutions-in-moles-per-cubic-decimetre-mt_vRK78ynnXb)

## Opens up

- [Rate Equations and Orders of Reaction](https://lightmysky.com/learn/science/rate-equations-and-orders-of-reaction-mt_1x3ogDKGxC)
- [The Haber Process and the Industrial Compromise](https://lightmysky.com/learn/science/the-haber-process-and-the-industrial-compromise-mt_J-JkijqnY5)
- [The Rate-Determining Step and Reaction Mechanisms](https://lightmysky.com/learn/science/the-rate-determining-step-and-reaction-mechanisms-mt_PM1Vo2CkVD)
- [Reversible Reactions, Dynamic Equilibrium and Le Chatelier](https://lightmysky.com/learn/science/reversible-reactions-dynamic-equilibrium-and-le-chatelier-mt_Zas-V3kTiR)