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Particulate Nature of Matter - Matter and Its Composition

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Matter is defined as anything that occupies space and has mass. It is composed of tiny particles called atoms or molecules.

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The Particulate Nature of Matter states that matter is not a continuous block but is made of discrete particles. This is evidenced by phenomena like the dissolution of sugar in H2OH_{2}O.

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Particles of matter have spaces between them, known as intermolecular spaces. In solids, this space is minimum, while in gases, it is maximum.

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Particles of matter are in continuous motion. This motion is called Brownian motion. The energy possessed by these particles due to their motion is known as Kinetic Energy (K.E.K.E.).

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The rate of diffusion increases with an increase in temperature because the Kinetic EnergyKinetic\ Energy of particles increases, causing them to move faster.

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Intermolecular Force of Attraction: The particles of matter attract each other with a force known as cohesive force. This force is strongest in solids and weakest in gases.

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States of Matter: Matter exists in three primary states: Solids (fixed shape and volume), Liquids (fixed volume, no fixed shape), and Gases (no fixed shape or volume).

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Diffusion is the spontaneous intermixing of particles of two different types of matter. For example, the spreading of the aroma of perfume or the smell of NH3NH_{3} in a room.

📐Formulae

Density(ρ)=Mass(m)Volume(V)Density (\rho) = \frac{Mass (m)}{Volume (V)}

T(K)=t(∘C)+273.15T(K) = t(^{\circ}C) + 273.15

K.E.∝TK.E. \propto T (Kinetic Energy is directly proportional to absolute Temperature)

Rate of Diffusion∝1Molar MassRate\ of\ Diffusion \propto \frac{1}{\sqrt{Molar\ Mass}}

💡Examples

Problem 1:

A substance has a mass of 500 g500\ g and occupies a volume of 250 cm3250\ cm^{3}. Calculate its density in g/cm3g/cm^{3}.

Solution:

Given: m=500 gm = 500\ g, V=250 cm3V = 250\ cm^{3}. Using the formula ρ=mV\rho = \frac{m}{V}, we get ρ=500250=2 g/cm3\rho = \frac{500}{250} = 2\ g/cm^{3}.

Explanation:

Density is the mass per unit volume of a substance, representing how closely particles are packed.

Problem 2:

Convert the room temperature of 25∘C25^{\circ}C into the Kelvin scale.

Solution:

T(K)=25+273.15=298.15 KT(K) = 25 + 273.15 = 298.15\ K.

Explanation:

The Kelvin scale is the SI unit of temperature, calculated by adding 273.15273.15 to the Celsius value.

Problem 3:

Why does a gas fill the vessel completely in which it is kept?

Solution:

In gases, the intermolecular force of attraction is negligible and Kinetic EnergyKinetic\ Energy is very high.

Explanation:

Because the particles have high K.E.K.E., they move randomly in all directions and occupy all available space due to weak cohesive forces.

Matter and Its Composition - Revision Notes & Key Formulas | CBSE Class 8 Science