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Matter and its Composition - States of Matter

Grade 7ICSE

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

🔑Concepts

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Matter is defined as anything that has mass, occupies space, and can be perceived by our senses. It is composed of tiny particles called atoms or molecules (H2OH_2O, O2O_2, etc.).

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The empty space between the particles of matter is known as Intermolecular Space. It is minimum in solids and maximum in gases.

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The force of attraction existing between the particles of matter is called Intermolecular Force of Attraction. It is strongest in solids and weakest in gases.

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Kinetic Theory of Matter states that particles of matter are in continuous random motion and possess Kinetic Energy (K.E.K.E.). The K.E.K.E. increases with an increase in temperature.

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Solids have a definite shape and a definite volume because the particles are closely packed with negligible intermolecular space and very strong intermolecular forces.

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Liquids have a definite volume but no definite shape. They take the shape of the container because the intermolecular forces are weaker than in solids, allowing particles to slide over each other.

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Gases have neither a definite shape nor a definite volume. They are highly compressible because of the large intermolecular spaces between particles.

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Change of State: Matter can change from one state to another by changing temperature or pressure. For example, Solid→MeltingLiquid→BoilingGasSolid \xrightarrow{Melting} Liquid \xrightarrow{Boiling} Gas.

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Sublimation is the process where a solid directly changes into a gas without passing through the liquid state (e.g., Camphor, NH4ClNH_4Cl).

📐Formulae

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

K.E.=12mv2K.E. = \frac{1}{2}mv^2

Total Energy=Potential Energy+Kinetic Energy\text{Total Energy} = \text{Potential Energy} + \text{Kinetic Energy}

H2O(s)→HeatH2O(l)→HeatH2O(g)H_2O_{(s)} \xrightarrow{\text{Heat}} H_2O_{(l)} \xrightarrow{\text{Heat}} H_2O_{(g)}

💡Examples

Problem 1:

If a substance has a mass of 500 g500\text{ g} and occupies a volume of 250 cm3250\text{ cm}^3, calculate its density.

Solution:

ρ=mV=500 g250 cm3=2 g/cm3\rho = \frac{m}{V} = \frac{500\text{ g}}{250\text{ cm}^3} = 2\text{ g/cm}^3

Explanation:

Density is the ratio of mass to volume. By dividing the given mass by the volume, we find the density of the substance.

Problem 2:

Explain why H2OH_2O (water) exists as a solid at 0∘C0^\circ C and as a gas at 100∘C100^\circ C based on the Kinetic Theory.

Solution:

At 0∘C0^\circ C, the K.E.K.E. of molecules is low, and intermolecular forces bind them into a fixed lattice (Ice). At 100∘C100^\circ C, molecules gain enough K.E.K.E. to overcome all intermolecular forces of attraction, moving independently as steam.

Explanation:

Temperature is directly proportional to the average kinetic energy of the particles. Higher temperature leads to state changes by overcoming attractive forces.

Problem 3:

Why can a gas be compressed easily while a solid cannot?

Solution:

Gases have very large intermolecular spaces compared to solids. Under pressure, these spaces can be reduced significantly.

Explanation:

In solids, particles are already so close together that there is no space to move them further inward. In gases, the distance between molecules is many times their own size.