Water vapour

Water in its gaseous state

For the use of water vapor in industrial applications, see Steam.

Water vapour (or water vapor) is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation.

Properties

Water vapor is a critical component of the Earth's atmosphere. It is invisible and is not the same as steam, which is water vapor that has condensed into small droplets. Water vapor is lighter than air and rises, contributing to the formation of clouds and precipitation.

Physical Properties

• Molecular Weight: 18.01528 g/mol
• Density: Approximately 0.804 g/L at 20°C and 1 atm
• Boiling Point: 100°C (212°F) at 1 atm

Chemical Properties

Water vapor is a polar molecule due to the bent shape of the water molecule, which results in a dipole moment. This polarity allows water vapor to interact with other polar molecules and ions, making it a good solvent in the gaseous state.

Role in the Atmosphere

Water vapor plays a significant role in the Earth's climate and weather systems. It is a potent greenhouse gas, absorbing and emitting infrared radiation, which contributes to the greenhouse effect.

Hydrological Cycle

Water vapor is a key component of the hydrological cycle. It evaporates from bodies of water, transpires from plants, and sublimates from ice and snow. Once in the atmosphere, it can condense to form clouds and eventually precipitate as rain or snow, returning to the Earth's surface.

Climate Impact

As a greenhouse gas, water vapor is responsible for about 50% of the Earth's natural greenhouse effect. It amplifies the effects of other greenhouse gases through a positive feedback loop: as the atmosphere warms, it can hold more water vapor, which in turn leads to more warming.

Measurement and Observation

Water vapor is measured using various instruments, including hygrometers, radiosondes, and satellites. These measurements are crucial for weather forecasting and climate modeling.

Applications

Water vapor is used in various industrial applications, including:

• Steam Power: Used to drive turbines in power plants.
• Humidification: Used to maintain humidity levels in controlled environments.
• Chemical Processes: Used as a reactant or solvent in chemical reactions.

Also see

• Evaporation
• Condensation
• Precipitation (meteorology)
• Greenhouse gas
• Hydrological cycle