Lesson Notes By Weeks and Term v4 - SHS 2
MATTER AND ITS PROPERTIES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
MATTER AND ITS PROPERTIES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Chemistry
Class: SHS 2
Term: 1st Term
Week: 3
Grade code: 2.1.1.LI.2
Strand code: 1
Sub-strand code: 1
Content standard code: 2.1.1.CS.1
Indicator code: 2.1.1.LI.2
Theme: PHYSICAL CHEMISTRY
Subtheme: MATTER AND ITS PROPERTIES
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
This lesson explores how we measure the energy stored in the substances all around us. In Ghana, we know that eating a ball of kenkey gives us energy to work, and burning charcoal provides the heat to cook our food. But how much energy, exactly? Chemistry provides us with a way to measure this energy through a technique called calorimetry. We will investigate the heat changes that occur during chemical reactions, such as burning fuels (combustion), mixing acids and bases (neutralization), and dissolving substances (solution).
2.1 What is Enthalpy Change (∆H)?
In almost every chemical reaction, energy is either released into the surroundings or absorbed from the surroundings. This energy is usually in the form of heat. Enthalpy (H) is a measure of the total heat content of a system at constant pressure. We cannot measure the absolute enthalpy of a substance directly. Enthalpy Change (∆H) is the heat energy change that occurs during a chemical reaction at constant pressure. It is the difference between the enthalpy of the products and the enthalpy of the reactants. ∆H = H(products) - H(reactants) 2.2 Exothermic and Endothermic Reactions
There are two main types of reactions based on heat change: Exothermic Reactions: These reactions release heat into the surroundings. The surroundings get hotter. The products have less enthalpy than the reactants. ∆H is negative (-). *Example:* Burning charcoal (combustion), mixing a strong acid and a strong base (neutralization). Think of "exo" as heat *exiting* the system. Endothermic Reactions: These reactions absorb heat from the surroundings. The surroundings get colder. The products have more enthalpy than the reactants. ∆H is positive (+). *Example:* Dissolving ammonium chloride (NH₄Cl) in water, photosynthesis. Think of "endo" as heat *entering* the system. 2.3 Calorimetry: Measuring Heat Changes
Calorimetry is the experimental technique used to measure the amount of heat involved in a chemical or physical process. A device used for this measurement is called a calorimeter. Principle: The fundamental principle is the conservation of energy. The heat released by the reaction (the *system*) is equal to the heat absorbed by the surroundings. Heat Released by Reaction = - (Heat Absorbed by Surroundings) A Simple Calorimeter: In our SHS lab, a simple calorimeter can be made from a polystyrene cup (or a metal can like a Milo tin), a lid, a thermometer, and a stirrer. We usually use a known mass of water as the surroundings to absorb the heat. 2.4 The Key Calculation: q = mc∆T