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Matter in Our Surroundings - Physical Nature of Matter

Grade 9CBSE

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

🔑Concepts

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Matter is anything that occupies space and has mass. The SI unit of mass is the kilogram (kgkg) and the SI unit of volume is the cubic metre (m3m^3).

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Physical Nature: Matter is made up of particles. These particles are extremely small, often measured at scales smaller than 10−9 m10^{-9} \text{ m}.

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Particles of matter have spaces between them. This is evidenced by the fact that when we dissolve salt in H2OH_2O, the particles of salt get into the spaces between the particles of water.

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Particles of matter are continuously moving and possess Kinetic Energy (EkE_k). As the temperature increases, the particles move faster because Ek∝TE_k \propto T.

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Diffusion: The process of intermixing of particles of two different types of matter on their own is called diffusion. The rate of diffusion increases with an increase in temperature.

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Particles of matter attract each other due to intermolecular forces. The strength of this force of attraction varies from one kind of matter to another (highest in solids, least in gases).

📐Formulae

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

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

1 L=1 dm3=10−3 m31 \text{ L} = 1 \text{ dm}^3 = 10^{-3} \text{ m}^3

1 mL=1 cm31 \text{ mL} = 1 \text{ cm}^3

💡Examples

Problem 1:

A small crystal of potassium permanganate (KMnO4KMnO_4) can color a large volume of water (1000 L1000 \text{ L}). What does this experiment prove about the nature of matter?

Solution:

This proves that matter is made of millions of tiny particles.

Explanation:

Even a tiny crystal of KMnO4KMnO_4 contains millions of particles. When dissolved, these particles keep on dividing themselves into smaller and smaller numbers, spreading throughout the H2OH_2O and imparting color to a large volume.

Problem 2:

The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close. Explain why using the concept of Kinetic Energy.

Solution:

Higher temperature leads to higher Kinetic Energy (EkE_k), resulting in faster diffusion.

Explanation:

At higher temperatures, the particles of the aroma of food move with higher velocity because their Kinetic Energy (Ek=12mv2E_k = \frac{1}{2}mv^2) increases. This causes them to diffuse into the air more rapidly and cover larger distances compared to particles at lower temperatures.

Problem 3:

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

Solution:

298.15 K298.15 \text{ K}

Explanation:

Using the formula T(K)=t(∘C)+273.15T(K) = t(^{\circ}C) + 273.15, we substitute the value: 25+273.15=298.15 K25 + 273.15 = 298.15 \text{ K}.

Physical Nature of Matter - Revision Notes & Key Formulas | CBSE Class 9 Science