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Introduction to Chemistry - States of Matter

Grade 7CBSE

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

🔑Concepts

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Matter is defined as anything that has mass and occupies space (volume). All matter is composed of tiny particles called atoms or molecules.

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The kinetic theory of matter states that particles are in constant motion. The degree of motion depends on the energy of the particles, which is usually related to temperature.

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Solids: Particles are closely packed in a fixed arrangement. They have a definite shape and volume. The intermolecular force of attraction is strongest in solids, and the intermolecular space is minimum.

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Liquids: Particles are less closely packed and can move past each other. They have a definite volume but no fixed shape (they take the shape of the container). The intermolecular force is weaker than in solids.

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Gases: Particles are far apart and move randomly at high speeds. They have neither a definite shape nor a definite volume. The intermolecular force is negligible, and the intermolecular space is maximum.

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Change of State: Matter can change from one state to another by absorbing or releasing heat. This includes Melting (Solid to Liquid), Vaporization (Liquid to Gas), Condensation (Gas to Liquid), Freezing (Liquid to Solid), and Sublimation (Solid to Gas directly).

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Diffusion: The intermixing of particles of two different types of matter on their own. It is fastest in gases and slowest in solids.

📐Formulae

Density=MassVolumeDensity = \frac{Mass}{Volume}

d=mVd = \frac{m}{V}

T(K)=T(∘C)+273T(K) = T(^{\circ}C) + 273

1 cm3=1 mL1 \text{ cm}^3 = 1 \text{ mL}

💡Examples

Problem 1:

An object has a mass of 450 g450\text{ g} and a volume of 150 cm3150\text{ cm}^3. Calculate the density of the object.

Solution:

Given: Mass (mm) = 450 g450\text{ g} Volume (VV) = 150 cm3150\text{ cm}^3

Using the formula: Density(d)=mVDensity (d) = \frac{m}{V} d=450150d = \frac{450}{150} d=3 g/cm3d = 3\text{ g/cm}^3

Explanation:

Density is calculated by dividing the mass of the substance by the volume it occupies. In this case, every cubic centimeter of the object weighs 3 grams.

Problem 2:

The boiling point of water is 100∘C100^{\circ}C. Convert this temperature into the Kelvin scale.

Solution:

Given: Temperature in Celsius (T∘CT_{^{\circ}C}) = 100∘C100^{\circ}C

Using the conversion formula: T(K)=T(∘C)+273T(K) = T(^{\circ}C) + 273 T(K)=100+273T(K) = 100 + 273 T(K)=373 KT(K) = 373\text{ K}

Explanation:

To convert from Celsius to Kelvin, we add 273273 to the Celsius value because 0∘C0^{\circ}C is equivalent to 273 K273\text{ K}.

Problem 3:

Calculate the total mass of a liquid if its density is 0.8 g/cm30.8\text{ g/cm}^3 and it fills a container of volume 250 cm3250\text{ cm}^3.

Solution:

Given: Density (dd) = 0.8 g/cm30.8\text{ g/cm}^3 Volume (VV) = 250 cm3250\text{ cm}^3

From the formula d=mVd = \frac{m}{V}, we can derive: m=d×Vm = d \times V m=0.8×250m = 0.8 \times 250 m=200 gm = 200\text{ g}

Explanation:

By rearranging the density formula, we can find the mass by multiplying the density of the liquid by its volume.