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States of Matter - Solids, Liquids, and Gases

Grade 6IB

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

🔑Concepts

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Matter is defined as anything that has mass (mm) and occupies space (volume, VV).

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The Kinetic Molecular Theory states that all matter is made of tiny particles (atoms or molecules) that are constantly in motion. The energy of this motion is called kinetic energy (EkE_k).

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Solids: Particles are packed closely together in a regular arrangement called a lattice. They vibrate about fixed positions, giving solids a fixed shape and volume.

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Liquids: Particles are close together but can slide past one another. They have a fixed volume but take the shape of the bottom of their container. Intermolecular forces are weaker than in solids.

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Gases: Particles are far apart and move randomly at high speeds. They have no fixed shape or volume and will expand to fill any container. They are easily compressed because of the large spaces between particles.

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Phase Changes: Changes in state occur when thermal energy is added or removed. For example, ice (H2O(s)H_2O_{(s)}) melts into liquid water (H2O(l)H_2O_{(l)}) when energy is absorbed.

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Density: A property that describes how much mass is contained in a given volume. It is expressed as ρ=mV\rho = \frac{m}{V}.

📐Formulae

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

Total Energy=Kinetic Energy(Ek)+Potential Energy(Ep)\text{Total Energy} = \text{Kinetic Energy} (E_k) + \text{Potential Energy} (E_p) theory

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

💡Examples

Problem 1:

A sample of unknown liquid has a mass of 120 g120\,g and occupies a volume of 60 cm360\,cm^3. Calculate the density (ρ\rho) of the liquid.

Solution:

ρ=mV=120 g60 cm3=2 g/cm3\rho = \frac{m}{V} = \frac{120\,g}{60\,cm^3} = 2\,g/cm^3

Explanation:

To find the density, we divide the total mass by the volume the substance occupies. The unit is expressed as grams per cubic centimeter.

Problem 2:

Describe what happens to the particles of nitrogen (N2N_2) as it changes from a liquid state at −196∘C-196^\circ C to a gaseous state at room temperature.

Solution:

The N2N_2 particles absorb thermal energy, increasing their kinetic energy (EkE_k). They move fast enough to overcome the attractive forces holding them together in the liquid phase, spreading far apart to move randomly in all directions.

Explanation:

This process is known as evaporation or boiling. In a gas, the distance between particles is much greater than in a liquid.

Problem 3:

Why can a 50 cm350\,cm^3 syringe filled with air be compressed, while a syringe filled with 50 cm350\,cm^3 of water (H2OH_2O) cannot?

Solution:

Air is a gas, and gas particles have large empty spaces between them. Applying pressure forces these particles closer together. In liquid H2OH_2O, particles are already touching, so there is no space to compress them further.

Explanation:

This demonstrates the property of compressibility, which is high in gases and almost zero in liquids and solids.

Solids, Liquids, and Gases - Revision Notes & Key Formulas | IB Grade 6 Science