Lesson Notes By Weeks and Term v4 - SHS 2
MATTER AND ITS PROPERTIES
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MATTER AND ITS PROPERTIES
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Subject: Chemistry
Class: SHS 2
Term: 1st Term
Week: 2
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
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This lesson introduces the concept of enthalpy change, which is the heat energy released or absorbed during chemical reactions. We experience these changes every day: the heat from a charcoal stove used to cook banku, the energy we get from eating fufu, or the cooling sensation when certain salts dissolve in water. By understanding and measuring these energy changes—a process called calorimetry—we can compare the efficiency of different fuels, understand the nutritional value of foods, and predict whether a reaction will produce or consume heat. This knowledge is fundamental to chemistry and has practical applications in industries from food science to engineering.
2.1 Enthalpy and Enthalpy Change (ΔH)
In simple terms, enthalpy (H) is the total heat content of a system. We cannot measure the absolute enthalpy of a substance directly. However, we can measure the enthalpy change (ΔH), which is the heat energy absorbed or released during a chemical reaction at constant pressure.
The unit for enthalpy change is the Joule (J) or kilojoule (kJ).
There are two main types of reactions based on enthalpy change: Exothermic Reactions: These reactions *release* heat energy into the surroundings. The surroundings get warmer. For exothermic reactions, ΔH is negative (-). *Example:* Burning charcoal (combustion), mixing a strong acid and a strong base (neutralization). `Reactants → Products + Heat Energy` Endothermic Reactions: These reactions *absorb* heat energy from the surroundings. The surroundings get colder. For endothermic reactions, ΔH is positive (+). *Example:* Dissolving ammonium chloride in water, photosynthesis. `Reactants + Heat Energy → Products` 2.2 Calorimetry: Measuring Heat Changes