A liquid is a sample of matter that conforms to the shape of a container in which it is held, and which acquires a defined surface in the presence of gravity. The term liquid is also used in reference to the state, or condition, of matter having this property.
The atom s or molecule s of matter in the liquid state are compressed as tightly as those of matter in the solid state, but the atoms or molecules in a liquid can move freely among each other. Examples of liquids are water at room temperature (approximately 20 ºC or 68 ºF), oil at room temperature, and alcohol at room temperature.
When a liquid is heated, the atoms or molecules gain kinetic energy . If the temperature becomes sufficiently high, the liquid becomes a gas , or it may react with chemicals in the environment. Water is an example of a liquid that becomes gaseous when it is heated gradually. Alcohol will combust (combined with oxygen in the atmosphere) if heated suddenly and dramatically.
When a liquid is cooled, the atoms or molecules lose kinetic energy. If the temperature becomes low enough, the liquid becomes a solid. Water is a good example. If cooled down, it freezes into ice.