Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Describe the collision theory of chemical reactions.
• Explain the factors that affect the rate of a reaction.
• Predict how temperature and catalysts change reaction rates.
• Sketch and interpret the Maxwell-Boltzmann energy distribution curve.

Lesson summary

Welcome, students! Today, we are going to explore one of the most fundamental questions in chemistry: *Why do some chemical reactions happen very fast, while others take a very long time?* Think about cooking yam in a pot. Why does it cook faster when the fire is very hot? Or why does powdered sugar dissolve in water much faster than a sugar cube? The answers lie in a powerful idea called the Collision Theory. Understanding this helps us control chemical reactions everywhere, from the food we cook in our kitchens to the medicines produced in pharmaceutical companies and the fuel refined at the Tema Oil Refinery.

Lesson notes

A. What is a Reaction Rate? Before we discuss why rates differ, let's define what a reaction rate is. Reaction Rate is the speed at which a chemical reaction occurs. It is measured as the change in the concentration of a reactant or a product per unit time. Fast reaction example: The explosion of a firecracker. Slow reaction example: The rusting of an iron gate. B. The Collision Theory For a chemical reaction to occur, the reacting particles (atoms, molecules, or ions) must interact. The Collision Theory provides a model to explain how these interactions lead to a reaction. It is based on two main points: Particles Must Collide: For a reaction to occur, the reactant particles must first collide with each other. Collisions Must Be Effective: Not every collision results in a chemical reaction. A collision is only effective (i.e., leads to the formation of products) if it meets two specific conditions: Condition 1: Sufficient Kinetic Energy: The colliding particles must have a certain minimum amount of kinetic energy. This minimum energy is called the Activation Energy (Ea). Activation Energy (Ea): The minimum amount of energy that colliding particles must possess for a reaction to occur. Think of it as a small hill that particles must have enough energy to climb over to get to the other side (the products). Condition 2: Correct Orientation: The colliding particles must be aligned in a specific way that allows the old bonds to break and new bonds to form. This is called the correct collision geometry or favourable orientation.

In summary: Rate of Reaction ∝ Frequency of Effective Collisions

The more effective collisions that happen in a given amount of time, the faster the reaction rate.

*Analogy:* Imagine you have a key (reactant 1) and a lock (reactant 2). For the lock to open (reaction), you must not only hit the lock with the key (a collision), but you must also hit it with enough force (activation energy) AND have the key pointing the right way (correct orientation). C. Factors Affecting the Rate of Reaction (Explained by Collision Theory)

Evaluation guide

• Describe the collision theory and use it to explain qualitatively, the effects of the
• factors that affect the rate of reaction .
• Collaborative Learning:
• In a class session, brainstorm on the interactions occurring in a chemical reacting system and