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States of Matter - The Particle Theory

Grade 6IGCSE

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

🔑Concepts

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Matter is made up of tiny particles (atoms or molecules such as H2OH_2O) that are constantly in motion.

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In a Solid, particles are packed closely together in a regular lattice arrangement; they vibrate about fixed positions and have the least kinetic energy (EkE_k).

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In a Liquid, particles are close together but arranged randomly; they can move and slide over each other, allowing liquids to flow and take the shape of the container bottom.

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In a Gas, particles are far apart and move rapidly and randomly in all directions; they have the most kinetic energy and can be easily compressed.

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Changes of State: Melting (Solid→LiquidSolid \rightarrow Liquid), Freezing (Liquid→SolidLiquid \rightarrow Solid), Boiling/Evaporation (Liquid→GasLiquid \rightarrow Gas), Condensation (Gas→LiquidGas \rightarrow Liquid), and Sublimation (Solid→GasSolid \rightarrow Gas).

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Temperature is a measure of the average kinetic energy of the particles; as temperature increases, particles move faster.

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Gas Pressure is caused by gas particles colliding with the walls of their container, exerting a force over an area (P=FAP = \frac{F}{A}).

📐Formulae

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

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

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

💡Examples

Problem 1:

A wooden cube has a mass of 200g200g and the length of one side is 5cm5cm. Calculate the density of the wood.

Solution:

Volume=5cm×5cm×5cm=125cm3\text{Volume} = 5cm \times 5cm \times 5cm = 125cm^3 Density=200g125cm3=1.6g/cm3\text{Density} = \frac{200g}{125cm^3} = 1.6g/cm^3

Explanation:

First, calculate the volume of the cube using V=l3V = l^3. Then, apply the density formula ρ=mV\rho = \frac{m}{V} to find the mass per unit volume.

Problem 2:

Explain why a gas can be compressed but a solid cannot, using the Particle Theory.

Solution:

In a gas, there are large spaces between the particles, allowing them to be pushed closer together. In a solid, the particles are already touching with no space between them.

Explanation:

The compressibility of a state of matter depends on the amount of empty space between its constituent particles.

Problem 3:

What happens to the particles of H2OH_2O when ice is heated until it becomes steam?

Solution:

As heat is added, the particles gain kinetic energy (EkE_k). In the solid state, they vibrate faster until they break the regular lattice (melting). As a liquid, they move faster until they overcome all attractive forces and move independently (boiling).

Explanation:

Adding thermal energy increases the motion of particles, eventually allowing them to overcome the intermolecular forces holding them in fixed positions.

The Particle Theory - Revision Notes & Key Formulas | IGCSE Grade 6 Science