What are States of Matter?
Matter exists in different physical states depending on how its particles are arranged and how freely they can move. The three common states of matter are solids, liquids, and gases. Each state has different properties because the particles have different amounts of energy, spacing, and freedom of movement.
Heating, cooling, or changing pressure can cause matter to change from one state to another.
Particle Model of Matter
All matter is made of tiny particles such as atoms or molecules.
These particles:
- are always moving
- have spaces between them
- attract one another
- move faster when heated
- move more slowly when cooled
The arrangement and movement of particles determine whether a substance behaves as a solid, liquid, or gas.
Solids
A solid has a fixed shape and a fixed volume.
The particles in a solid are packed closely together in an orderly arrangement. Strong attractive forces hold them in nearly fixed positions. The particles cannot move freely, but they vibrate about their positions.
Because the particles are closely packed, solids are difficult to compress.
Examples of solids include ice, wood, stone, glass, metal, and plastic.
Properties of Solids
- fixed shape
- fixed volume
- particles packed closely together
- strong forces of attraction
- particles vibrate in fixed positions
- difficult to compress
Liquids
A liquid has a fixed volume, but it does not have a fixed shape.
The particles in a liquid are close together but are not held in fixed positions. They can move and slide past one another, allowing the liquid to flow and take the shape of its container.
Liquids are difficult to compress because there is little space between their particles.
Examples include water, milk, oil, petrol, and mercury.
Properties of Liquids
- fixed volume
- no fixed shape
- take the shape of their container
- particles remain close together
- particles can move past one another
- can flow
- difficult to compress
Gases
A gas has no fixed shape and no fixed volume.
The particles in a gas are far apart and move freely in all directions. The attractive forces between them are very weak.
A gas spreads out to fill the entire container in which it is placed. Gases can also be compressed because large spaces exist between their particles.
Examples include oxygen, nitrogen, carbon dioxide, hydrogen, and water vapour.
Properties of Gases
- no fixed shape
- no fixed volume
- fill the available container
- particles are far apart
- particles move rapidly and randomly
- weak forces of attraction
- easily compressed
Changes of State
Matter can change from one physical state to another when it gains or loses thermal energy.
During a change of state, the substance remains the same, but the arrangement and movement of its particles change.
The main changes of states are::
- Melting
- Freezing
- Evaporation and Boiling
- Condensation
- Sublimation
- Deposition
Melting
Melting is the change from a solid to a liquid.
When a solid is heated, its particles gain energy and vibrate more strongly. At the melting point, the particles overcome some of the forces holding them in fixed positions and begin to move past one another.
Ice melting into water is an example.
Freezing
Freezing is the change from a liquid to a solid.
When a liquid is cooled, its particles lose energy and move more slowly. They become arranged in fixed positions, forming a solid.
Water freezing into ice is an example.
Evaporation and Boiling
Evaporation and boiling both change a liquid into a gas.
Evaporation occurs at the surface of a liquid and can happen at temperatures below its boiling point. The fastest-moving particles escape from the liquid surface.
Boiling occurs throughout the liquid at a particular temperature called the boiling point.
Water changing into water vapour is an example.
Condensation
Condensation is the change from a gas to a liquid.
When a gas cools, its particles lose energy, move more slowly, and come closer together.
Water droplets forming on the outside of a cold glass are produced by condensation.
Sublimation
Sublimation is the direct change from a solid to a gas without passing through the liquid state.
Dry ice and camphor are substances that can undergo sublimation.
Deposition
Deposition is the direct change from a gas to a solid without becoming a liquid first.
The formation of frost from water vapour is an example of deposition.
Changes of State and Energy
A substance absorbs energy during:
- melting
- evaporation
- boiling
- sublimation
A substance releases energy during:
- freezing
- condensation
- deposition
During the actual change of state, the temperature may remain constant even though energy continues to be transferred. The energy is used to change the arrangement of particles rather than increase their speed.
Effect of Pressure
Pressure can also affect the state of matter.
Increasing the pressure on a gas forces its particles closer together. Under suitable conditions, this can cause the gas to become a liquid.
Liquefied petroleum gas, or LPG, is stored as a liquid under pressure inside cylinders.
Plasma
Plasma is a high-energy state of matter made of charged particles.
It forms when a gas receives enough energy for electrons to separate from atoms. Plasma can conduct electricity and is affected by electric and magnetic fields.
The Sun, stars, lightning, and fluorescent lamps contain plasma.
States of Matter in Everyday Life
Changes of state occur all around us:
- ice melts in a warm room
- water freezes inside a freezer
- wet clothes dry by evaporation
- steam condenses on a cool surface
- water boils during cooking
- frost forms on cold surfaces
Understanding states of matter helps explain weather, cooking, refrigeration, industrial processes, and many natural phenomena.
Key Points
Matter commonly exists as solids, liquids, and gases.
A solid has a fixed shape and volume. A liquid has a fixed volume but takes the shape of its container. A gas has neither a fixed shape nor a fixed volume.
Changes in temperature and pressure can alter the physical state of matter. These changes are physical changes because no new substance is formed.
Glossary of Key Terms
Recap of the Key Terms in States of Matter
- Boiling Point: The temperature at which a liquid boils and changes into a gas.
- Boiling: The rapid change of a liquid into a gas throughout the liquid.
- Change of State: A physical change in which matter changes from one state to another.
- Compressibility: The ability of a substance to decrease in volume when pressure is applied.
- Condensation: The change of state from a gas to a liquid.
- Deposition: The direct change of state from a gas to a solid without passing through the liquid state.
- Diffusion: The spreading of particles from a region of higher concentration to a region of lower concentration.
- Evaporation: The change of a liquid into a gas at its surface, usually below the boiling point.
- Force of Attraction: The force that pulls particles towards one another.
- Freezing Point: The temperature at which a liquid changes into a solid.
- Freezing: The change of state from a liquid to a solid.
- Gas: A state of matter with no fixed shape and no fixed volume.
- Liquid: A state of matter with a fixed volume but no fixed shape.
- LPG: Liquefied petroleum gas stored as a liquid under pressure.
- Matter: Anything that has mass and occupies space.
- Medium: A substance through which particles or energy may move.
- Melting Point: The temperature at which a solid changes into a liquid.
- Melting: The change of state from a solid to a liquid.
- Particle Model of Matter: A model that explains the properties of matter using the arrangement, movement, and energy of its particles.
- Particle: A tiny unit of matter, such as an atom or molecule.
- Physical Change: A change in which no new substance is formed.
- Plasma: A high-energy state of matter made of positively charged ions and free electrons.
- Pressure: The force acting on a unit area of a surface.
- Shape: The external form or outline of an object.
- Solid: A state of matter with a fixed shape and fixed volume.
- State of Matter: The physical form in which matter exists, such as a solid, liquid, or gas.
- Sublimation: The direct change of state from a solid to a gas without passing through the liquid state.
- Thermal Energy: The energy associated with the movement of particles in a substance.
- Volume: The amount of space occupied by an object or substance.
- Water Vapour: Water in its gaseous state.
Questions and Answers
Recap the concepts you have learnt. Try to answer the questions. You can find the answer to any question by clicking on the icon.
What are the three common states of matter?
The three common states of matter are solids, liquids, and gases.
What determines the state of matter?
The arrangement, movement, spacing, and energy of particles determine the state of matter.
What are the main properties of a solid?
A solid has a fixed shape and fixed volume. Its particles are closely packed and vibrate in fixed positions.
Why are solids difficult to compress?
Solids are difficult to compress because their particles are packed very closely together.
What are the main properties of a liquid?
A liquid has a fixed volume but no fixed shape. It flows and takes the shape of its container.
Why can liquids flow?
Liquids can flow because their particles can move and slide past one another.
What are the main properties of a gas?
A gas has no fixed shape and no fixed volume. It spreads out to fill its container.
Why are gases easy to compress?
Gases are easy to compress because there are large spaces between their particles.
What is a change of state?
A change of state is a physical change in which matter changes from one state to another.
What happens to particles when matter is heated?
The particles gain energy and move faster.
What happens to particles when matter is cooled?
The particles lose energy and move more slowly.
What is melting?
Melting is the change of state from a solid to a liquid.
What is freezing?
Freezing is the change of state from a liquid to a solid.
What is evaporation?
Evaporation is the change of a liquid into a gas at its surface, usually below the boiling point.
How is boiling different from evaporation?
Evaporation occurs only at the surface and can happen below the boiling point. Boiling occurs throughout the liquid at a particular temperature.
What is condensation?
Condensation is the change of state from a gas to a liquid.
What is sublimation?
Sublimation is the direct change from a solid to a gas without passing through the liquid state.
What is deposition?
Deposition is the direct change from a gas to a solid without passing through the liquid state.
Give an example of melting.
Ice changing into water is an example of melting.
Give an example of freezing.
Water changing into ice is an example of freezing.
Give an example of condensation.
Water droplets forming on the outside of a cold glass are an example of condensation.
Give an example of sublimation.
Dry ice changing directly into carbon dioxide gas is an example of sublimation.
Give an example of deposition.
Frost forming directly from water vapour is an example of deposition.
During which changes of state is energy absorbed?
Energy is absorbed during melting, evaporation, boiling, and sublimation.
During which changes of state is energy released?
Energy is released during freezing, condensation, and deposition.
Why does the temperature of a substance remain constant during melting or boiling?
During melting or boiling, the energy supplied is used to overcome the attractive forces between particles and change their arrangement, rather than increase their kinetic energy. Therefore, the temperature remains constant until the change of state is complete.
How does pressure affect gases?
Increasing pressure pushes gas particles closer together and may cause the gas to become a liquid.
What is plasma?
Plasma is a high-energy state of matter made of charged particles.
Where is plasma found?
Plasma is found in the Sun, stars, lightning, and fluorescent lamps.
Is a change of state a physical or chemical change?
It is a physical change because no new substance is formed.