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: 19
Grade code: 1.1.1.LI.3
Strand code: 1
Sub-strand code: 1
Content standard code: 1.1.1.CS.3
Indicator code: 1.1.1.LI.3
Theme: PHYSICAL CHEMISTRY
Subtheme: MATTER AND ITS PROPERTIES
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Welcome, future scientists and engineers! Today, we delve into the fascinating world of gases. Have you ever wondered why you can smell your mother’s delicious *kelewele* or *waakye* from across the compound even before you enter the kitchen? Or why a punctured car tyre goes flat? The answers lie in the constant, random motion of gas particles. This lesson explores two fundamental laws that govern this behaviour: Graham's Law, which explains the speed at which gases spread out, and Dalton's Law, which helps us understand the pressure in a mixture of gases, like the very air we breathe.
This section breaks down the core ideas you need to master. Pay close attention to the definitions and the step-by-step calculations. Part A: Graham's Law of Diffusion and Effusion Key Definitions Diffusion: The process by which particles of a substance (gas, liquid, or solid) spread out from a region of higher concentration to a region of lower concentration, due to their random motion. *Simple Analogy:* Spraying perfume in one corner of the classroom. Eventually, students in the opposite corner will smell it because the perfume particles have mixed with the air particles and spread throughout the room. Effusion: The process by which gas particles escape from a container through a very tiny hole or orifice into a vacuum or a region of lower pressure. *Simple Analogy:* The gradual loss of air from a bicycle or car tyre that has a small, invisible puncture. Stating Graham's Law
Graham's Law of Diffusion states that, under the same conditions of temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass or its density.
This means that lighter gases (with lower molar mass) diffuse faster, while heavier gases (with higher molar mass) diffuse slower. Mathematical Expressions of Graham's Law
Let's consider two gases, Gas 1 and Gas 2. Let: `r₁` and `r₂` be their rates of diffusion/effusion. `M₁` and `M₂` be their molar masses. `d₁` and `d₂` be their densities.