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vapour

Primary Information
Secondary Information

Definition

Vapour is a gaseous state of a substance that is below its boiling point. It is formed when the molecules of a liquid or solid have enough energy to overcome the forces of attraction between them.

The amount of vapour in a given space depends on the temperature and pressure of the gas. The higher the temperature, the more vapour can be present. The lower the pressure, the more vapour can be present.

Vapour can be converted back into a liquid by condensation. This happens when the temperature of the vapour is lowered or the pressure is increased.

How can the word be used?

The fog was a thick vapour that obscured the view.

vapour

Different forms of the word

Noun:

  • a substance in the gaseous state at a temperature below its boiling point.
  • a visible mist or cloud of such a substance.

Verb:

  • to change from a liquid or solid to a gaseous state.
  • to give off vapour.

Etymology

The word "vapour" comes from the Old French word "vapor", which also means "a substance in the gaseous state at a temperature below its boiling point".

The first recorded use of the word "vapour" in English was in the 14th century.

Question

Where might you find vapour?

AQA Science Exam Question and Answer

Question:

Define vaporisation and explain how it differs from evaporation. Provide an example of a natural process where vaporisation plays a crucial role.

Answer:

Vaporisation is the phase transition process in which a liquid substance changes into its gaseous state. It involves the absorption of energy, usually in the form of heat, to break the intermolecular forces holding the liquid molecules together. Vaporisation can occur through two main mechanisms: evaporation and boiling.

Evaporation is a specific type of vaporisation that occurs at the surface of a liquid, where molecules with higher kinetic energy escape into the air. It happens at temperatures below the liquid's boiling point and is influenced by factors like temperature, surface area, and humidity.

Boiling, on the other hand, is a more rapid form of vaporisation that occurs throughout the entire liquid when its internal pressure equals the atmospheric pressure. It happens at a specific temperature known as the boiling point.

A natural process where vaporisation plays a crucial role is the water cycle. As sunlight heats up bodies of water like lakes, rivers, and oceans, water molecules at the surface gain enough energy to overcome intermolecular forces and evaporate into water vapour. This vapour rises into the atmosphere, where it cools and condenses to form clouds. Subsequently, the accumulated water droplets in clouds can re-vaporise through processes like sublimation and evaporation, eventually leading to precipitation in the form of rain or snow, which replenishes Earth's water sources.