States of Matter - Solids, Liquids and Gases

Objective

Describe changes of state in terms of melting, boiling, evaporating, freezing and condensing.

Introduction

Matter exists in different states, the most common being solid, liquid, and gas. These states are distinguished by the arrangement and movement of their constituent particles (atoms or molecules). Changes of state occur when energy is added or removed from a substance.

States of Matter

The three common states of matter are:

• Solid: Definite shape and volume. Particles are closely packed and vibrate in fixed positions.
• Liquid: Definite volume but no definite shape. Particles are close together but can move past each other.
• Gas: No definite shape or volume. Particles are widely separated and move randomly.

Changes of State

Melting

Melting is the change of state from solid to liquid. This occurs when the temperature of the solid reaches its melting point. Energy (in the form of heat) is added to the solid, increasing the kinetic energy of the particles, overcoming the intermolecular forces holding them in a fixed position.

Example: Ice melting into water.

Freezing

Freezing is the change of state from liquid to solid. This occurs when the temperature of the liquid reaches its freezing point. Energy (in the form of heat) is removed from the liquid, decreasing the kinetic energy of the particles, allowing intermolecular forces to hold them in a fixed position.

Example: Water freezing into ice.

Boiling

Boiling is the change of state from liquid to gas. This occurs when the temperature of the liquid reaches its boiling point. Energy (in the form of heat) is added to the liquid, increasing the kinetic energy of the particles sufficiently for them to overcome the intermolecular forces and escape into the gaseous phase.

Example: Water boiling into steam.

Condensing

Condensing is the change of state from gas to liquid. This occurs when the temperature of the gas decreases. The kinetic energy of the particles decreases, allowing intermolecular forces to pull them closer together and form a liquid.

Example: Steam condensing into water droplets on a cold surface.

Evaporating

Evaporating is the change of state from liquid to gas. This occurs when liquid particles gain enough kinetic energy to overcome the intermolecular forces holding them together and escape into the gaseous phase. Evaporation can occur at temperatures below the boiling point.

Example: Water evaporating from a puddle.

Phase Changes and Energy

Changes of state involve the absorption or release of energy. This energy is known as the latent heat. There are two types of latent heat:

1. Latent heat of fusion: The energy required to change a substance from solid to liquid (melting) or vice versa (freezing) at a constant temperature.
2. Latent heat of vaporization: The energy required to change a substance from liquid to gas (boiling) or vice versa (condensation) at a constant temperature.

Summary Table

Change of State	Process	Energy Change	Temperature
Melting	Solid to Liquid	Energy Absorbed	Melting Point
Freezing	Liquid to Solid	Energy Released	Freezing Point
Boiling	Liquid to Gas	Energy Absorbed	Boiling Point
Condensing	Gas to Liquid	Energy Released	Condensation Point
Evaporating	Liquid to Gas	Energy Absorbed	Occurs at any temperature below the boiling point