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States of Matter - Particle Theory

Grade 6IB

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

🔑Concepts

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All matter is composed of tiny, discrete particles known as atomsatoms or moleculesmolecules.

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Particles in a Solid are tightly packed in a regular pattern (lattice), vibrating around fixed positions with strong forces of attraction.

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Particles in a Liquid are close together but arranged randomly; they have enough energy to slide past one another, allowing liquids to flow.

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Particles in a Gas are far apart, move rapidly in random directions, and have negligible forces of attraction between them.

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The kinetic energy (EkE_k) of particles increases with temperature (TT); as a substance is heated, its particles move faster.

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Phase changes, such as melting (H2O(s)ightarrowH2O(l)H_2O_{(s)} ightarrow H_2O_{(l)}) or boiling (H2O(l)ightarrowH2O(g)H_2O_{(l)} ightarrow H_2O_{(g)}), occur when energy is added to overcome the attractive forces between particles.

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Diffusion is the process where particles spread out from an area of high concentration to an area of low concentration due to their random motion.

📐Formulae

Density(ρ)=mass(m)volume(V)\text{Density} (\rho) = \frac{\text{mass} (m)}{\text{volume} (V)}

Ek∝TE_k \propto T

Pressure(P)=Force(F)Area(A)\text{Pressure} (P) = \frac{\text{Force} (F)}{\text{Area} (A)}

H2O(s)→meltingH2O(l)→boilingH2O(g)H_2O_{(s)} \xrightarrow{\text{melting}} H_2O_{(l)} \xrightarrow{\text{boiling}} H_2O_{(g)}

💡Examples

Problem 1:

Explain why a balloon filled with air expands when placed in a warm environment.

Solution:

The particles inside the balloon gain thermal energy, increasing their kinetic energy (EkE_k).

Explanation:

According to particle theory, as temperature (TT) increases, the gas particles move faster and collide with the walls of the balloon more frequently and with more force, pushing the walls outward.

Problem 2:

Compare the density (ρ\rho) of ice (H2O(s)H_2O_{(s)}) and water vapor (H2O(g)H_2O_{(g)}).

Solution:

ρice>ρvapor\rho_{ice} > \rho_{vapor}

Explanation:

In a solid like ice, the particles are closely packed together, meaning there is more mass (mm) in a given volume (VV). In a gas, the particles are widely spaced, meaning there is very little mass in the same volume.

Problem 3:

What happens to the arrangement of particles during the process of sublimation, such as with dry ice (CO2(s)→CO2(g)CO_{2(s)} \rightarrow CO_{2(g)})?

Solution:

Particles transition from a fixed, ordered lattice directly into a high-energy, random, and widely dispersed state.

Explanation:

Sublimation involves the particles gaining enough energy to completely overcome all attractive forces in the solid state without passing through the liquid phase.