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States of Matter - The behavior of particles in solids, liquids, and gases

Grade 5IGCSE

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

🔑Concepts

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Matter is everything around us that has mass and takes up space. It is composed of tiny particles, often represented as spheres in the particle model.

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The Kinetic Theory of Matter states that particles are in constant motion. The amount of motion depends on the amount of energy (heat) the particles possess.

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In a solid, particles are packed tightly together in a regular, fixed arrangement called a lattice. They can only vibrate about their fixed positions, which is why solids have a fixed shape and volume.

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In a liquid, particles are close together but arranged randomly. They have enough energy to slide over each other, allowing liquids to flow and take the shape of the bottom of their container while maintaining a fixed volume.

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In a gas, particles are far apart and move rapidly in random directions. There are large spaces between particles, allowing gases to be compressed and to fill the entire volume of any container.

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Changes of state involve energy transfers. For example, when H2O(s)H_2O(s) (ice) is heated, the particles gain kinetic energy until they can break free from the fixed lattice to become H2O(l)H_2O(l) (liquid water).

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Pressure in gases is caused by the particles colliding with the walls of the container. The more frequent and forceful the collisions, the higher the pressure (PP).

📐Formulae

Density=MassVolume\text{Density} = \frac{\text{Mass}}{\text{Volume}}

Melting Point of H2O=0∘C\text{Melting Point of } H_2O = 0^\circ C

Boiling Point of H2O=100∘C\text{Boiling Point of } H_2O = 100^\circ C

K=∘C+273.15K = ^\circ C + 273.15

💡Examples

Problem 1:

A student has a sealed balloon filled with air. When the student squeezes the balloon, the volume decreases. Explain this behavior using the particle model of a gas.

Solution:

Gases are easily compressed because there is a lot of empty space between the particles. Squeezing the balloon pushes the particles closer together, decreasing the total volume occupied by the gas.

Explanation:

In a gas, the particles are not touching. The distance between particles is much larger than the size of the particles themselves. Applying pressure forces these particles into a smaller space.

Problem 2:

What happens to the particles of H2OH_2O when liquid water is heated to 100∘C100^\circ C?

Solution:

The particles gain enough kinetic energy to overcome the attractive forces holding them together in the liquid state. They break away and move rapidly and independently as H2O(g)H_2O(g) (steam).

Explanation:

This process is called boiling. The energy added as heat increases the movement of the particles until they transition from the liquid phase to the gaseous phase.

Problem 3:

A solid block has a mass of 200g200g and a volume of 50cm350cm^3. Calculate its density.

Solution:

Density=200g50cm3=4g/cm3\text{Density} = \frac{200g}{50cm^3} = 4g/cm^3

Explanation:

Density measures how much mass is packed into a specific volume. In solids, because particles are very close together, the density is usually higher than in gases.