Lesson Notes By Weeks and Term v4 - SHS 3
MATTER AND ITS PROPERTIES
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MATTER AND ITS PROPERTIES
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Subject: Chemistry
Class: SHS 3
Term: 1st Term
Week: 18
Grade code: 1.1.1.LI.2
Strand code: 1
Sub-strand code: 1
Content standard code: 1.1.1.CS.3
Indicator code: 1.1.1.LI.2
Theme: PHYSICAL CHEMISTRY
Subtheme: MATTER AND ITS PROPERTIES
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This lesson introduces the fundamental laws that describe the behaviour of gases. We encounter gases every day in Ghana – from the LPG we use for cooking to the air in our car tyres and the bubbles in a fizzy drink. Understanding how gases behave when conditions like temperature, pressure, or volume change is crucial not only for chemistry but also for many real-world applications in engineering, medicine, and meteorology. We will explore the relationships between pressure, volume, temperature, and the amount of a gas, and learn how to use these relationships to make predictions and perform calculations.
A. The Nature of Gases and Key Variables
Before we study the laws, let's remember the Kinetic Theory of Gases. It states that gases consist of tiny particles that are in constant, random, straight-line motion. They are far apart, and the forces between them are negligible. The energy of these particles depends on temperature.
To describe a gas, we use four main variables: Pressure (P): The force exerted by the gas per unit area of its container. It's caused by the gas particles colliding with the container walls. *Units:* atmospheres (atm), millimeters of mercury (mmHg), pascals (Pa). `1 atm = 760 mmHg = 101,325 Pa`. Volume (V): The space occupied by the gas, which is equal to the volume of its container. *Units:* litres (L), millilitres (mL), cubic centimetres (cm³), cubic metres (m³). `1 L = 1000 cm³ = 1 dm³`. Temperature (T): A measure of the average kinetic energy of the gas particles. In all gas law calculations, temperature must be in the Kelvin (K) scale. *Conversion:* `Kelvin (K) = Celsius (°C) + 273`. Amount of Substance (n): The quantity of gas, measured in moles. *Unit:* moles (mol). B. Boyle's Law: The Pressure-Volume Relationship
Robert Boyle discovered that for a fixed amount of gas at a constant temperature, the volume is inversely proportional to the pressure. In simple words: If you squeeze a gas (increase pressure), its volume decreases. If you give it more space (decrease pressure), its volume increases. Statement: The volume (V) of a fixed mass of gas is inversely proportional to its pressure (P), provided the temperature (T) remains constant. Mathematical Expression: V ∝ 1/P (at constant n and T) V = k/P (where k is a constant) PV = k For a change from an initial state (1) to a final state (2): P₁V₁ = P₂V₂ Graphical Representation: A graph of P vs. V gives a downward curve (a hyperbola). A graph of P vs. 1/V gives a straight line passing through the origin.