Science class online
Chemistry and physics lessons
atom physics lesson


Free online chemistry lesson for elementary school, middle school and high school.
chemistry high school

Science class




Mechanics lessons
Water on Earth
Changes of state in the nature: the water cycle
Water in human body
Test for water
Properties of water in different states
States of matter
States of matter and its changes
Boiling water
Water: freezing and melting
Changes of state: mass and volume
Molecules in different states of matter

Mixtures and solutions
Heterogeneous mixtures
Homogeneous mixtures
Vaporization of water
Dissolving a solid in water
Conservation of mass on dissolving
Miscibility in water

Mass and volume
Volume and its units
Measuring volume with a graduated cylinder
Mass and its units
Measuring the mass of a liquid
Mass of a liter of water

Air and atmosphere
Earth's atmosphere protect us
Threats to the Earth's atmosphere
Composition of air
Air and life
Atoms and molecules
Molecules in mixtures and pure substances
Molecules and states of matter
Composition of molecules
Constituents of the atoms
The electrical neutrality of the atom

Basics of combustion
The combustion of carbon
The combustion of butane
Atoms and chemical reactions
Chemical reactions
Chemical equations
Law of conservation of mass
Chemical synthesis

Most common metals

How to distinguish metals ?

Corrosion of metals

Electrical conductivity of solid materials

Electrons and free electrons

Electric current in metals
The conductivity of aqueous solutions
Aqueous solutions and ions
The direction of movement of ions
Formation of ions
Tests for ions
Acidic and basic solutions
pH of aqueous solutions
Ions in acidic and basic solutions
Dilution of acids and bases
Composition of hydrochloric acid
Chemical reaction between iron and hydrochloric acid

Electrochemical cells and chemical energy
Chemical reaction beteween a copper sulphate solution and zinc
Copper sulfate and zinc battery
Basics of electrochemical cell


Sates of matter

States of matter and their changes


The essential about states of matter and their changes

The three states of matter

We distinguish for water and other substances three different states: Solid, liquid and gaseous states.
- In the solid state there are glaciers, sea ices, hail and snow ( composed of tiny ice crystals ).
- In the liquid state there are rivers, seas, oceans, rain,  and also clouds and fogs (composed of tiny water droplets ).
- In the gaseous state there is water vapor always invisible to the naked eye.


Changes of states

Water can change its state if temperature varies and under the action of Sun and wind.

Diagram: different  changes of state
Changes of states

- Melting (or fusion): transition from solid to liquid state.
- Vaporization: transition from liquid to gaseous state.
- Liquefaction (or condensation): transition from gaseous to liquid state.
- Solidification ( or freezing ): transition from liquid to solid state.
- Sublimation: transition from solid to gaseous state.
- Deposition: transition from gaseous to solid state.

The vaporization of a liquid may be gradual and natural (such as when exposed to sunlight ). We then say that there is " evaporation ". It can also be obtained by a rapid temperature rise which causes the formation of gas bubbles: this is called " boiling ".



Learn more about states of matter and changes of state

- Sates of matter: The three states and their properties at molecular scale ( with animations to explain the molecules move in solids, liquids and gases )

- Solids and liquids: A game which purpose is to shows differences between solid state and liquid state.

- Changing states: a flash game about changes of state

- States of water worksheet: A worksheet for kids where blank must be filled with changes of state ( evaporates, freeze, boils ...)

- Change of state worsheet: a three pages worksheet about three states, changes of states, energy and molecules.

- States of matter activities: a pdf document that provide various activities like card game about solids, liquids and gases, or a game board.

- Changing states game: a flash game in arctic about water and changes of state.

- States of matter experiment: Various experiments explained with videos