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Why is an explosion over in a flash while rusting takes years? Meet the factors that change reaction rate, the collision theory that explains all of them, and how to measure a rate in the lab.
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Fast and slow reactions ⏱️
Some reactions are over in a flash, like an explosion; others, like iron rusting, take years. The **rate** of a reaction is how quickly reactants turn into products. This module covers the **factors** that change the rate, the **collision theory** that explains them all, and how to measure a rate in the lab.
Key terms 🔑
Four ideas run through the topic:
What must happen to react? 💥
According to collision theory, what must happen for particles to react?
- They must collide with at least the activation energy
- They must simply be in the same container
- They must be heated to boiling point every time
- A catalyst must always be present
Match each factor to its reason 🔗
- Higher concentration
- Higher temperature
- Larger surface area
- Adding a catalyst
- More particles in a space means more frequent collisions
- Particles move faster and collide more often and more energetically
- A powder exposes more particles for collisions
- It lowers the activation energy needed to react
One idea explains them all 🧭
The clever part is that **collision theory** explains **every** factor. A reaction speeds up whenever collisions become **more frequent** or **more energetic**. Higher **concentration** and a larger **surface area** give more frequent collisions; a higher **temperature** makes collisions both more frequent and more energetic; a **catalyst** lowers the **activation energy**, so more collisions succeed. Learn the one idea, and every factor follows.
Which increase the rate? ✅
Select the TWO changes that would increase the rate of a reaction.
- Warming the reaction mixture up
- Using a powder instead of large lumps
- Diluting the acid with water
- Cooling the mixture in ice
Two ways to measure rate ⚗️
Core Practical 7.1 measures a rate in two different ways.
Run the practical 🪜
An interactive activity.
Reading a rate graph 📖
A graph of gas volume against time shows the rate at a glance:
Plot the rate curve 📈
An interactive activity.
Read the graph 🎯
On a graph of gas volume against time, what does a steeper line show?
- A faster rate of reaction
- A slower rate of reaction
- That the reaction has stopped
- Nothing at all about the rate
Complete the picture 🧱
The _____ of a reaction is how quickly products are made. Collision theory says particles must collide with enough energy, called the _____ energy. Increasing the _____ or the surface area gives more frequent collisions, while a _____ lowers the activation energy. On a rate graph, a steeper line means a _____ rate.
Predict the change 🔀
An interactive activity.
Explain with collision theory ✍️
An interactive activity.