Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Explain the factors affecting reaction rates
• Investigate these factors through experiments
• Analyze experimental data and graphs
• Discuss real-life applications of reaction rates

Lesson summary

This lesson explores the fascinating topic of reaction rates, which is essentially the "speed" of a chemical reaction. In our daily lives in Ghana, we see this principle everywhere: why does yam cook faster when cut into smaller pieces? Why do we keep fresh fish on ice to prevent it from spoiling? Why does a coal pot fire burn more fiercely when we fan it with air? Understanding the factors that control the speed of reactions allows us to control chemical processes, from cooking our food to manufacturing essential products and even understanding how our own bodies work.

Lesson notes

2.1 What is the Rate of a Reaction?

Just like a car's speed is measured by the distance it travels in a certain time (km/h), a reaction's rate is measured by how much a reactant is used up or how much a product is formed in a specific period. Definition: The rate of a chemical reaction is the change in the concentration of a reactant or a product per unit time. Formula: Rate = (Change in amount of substance) / (Time taken) or Rate = (Change in concentration of substance) / (Time taken) Units: The units depend on what is being measured. Common units include: moles per second (mol/s) grams per second (g/s) cubic centimetres per second (cm³/s) moles per decimetre cubed per second (mol/dm³/s) How We Measure Reaction Rates

To find the rate, we must be able to measure a change over time. Common methods include: Measuring the volume of gas produced: For reactions that produce a gas (like H₂ or CO₂), we can collect the gas in a gas syringe or a measuring cylinder over water and record the volume at regular time intervals (e.g., every 30 seconds). Measuring the loss in mass: If a reaction produces a gas that is allowed to escape, the total mass of the flask and its contents will decrease. We can place the flask on a digital balance and record the mass at regular intervals. Measuring the time for a visible change: Some reactions have a clear endpoint. For example, the formation of a precipitate that obscures a mark (like in the "sulphur-clock" experiment) or a distinct colour change. We measure the time it takes for this change to occur. 2.2 The Collision Theory

For a chemical reaction to occur between reactant particles (atoms, ions, or molecules), three conditions must be met. This is the Collision Theory. Collision: The reactant particles must collide with each other. Sufficient Energy: The colliding particles must have a minimum amount of kinetic energy, known as the Activation Energy (Ea). This energy is needed to break the existing bonds in the reactants so that new bonds can form. Correct Orientation: The particles must collide in the correct spatial arrangement, or orientation, for the bonds to break and reform effectively.

Evaluation guide

• Perform experiments to investigate the factors that affect the rate of reaction and
• analys e the data from the rate experiments.
• Experiential Learning :
• In small mixed -ability groups and using circus activities, design, and perform experiments to