Water in the Air

It’s always there

Water is ALWAYS in the Air!

• It can be in the air as a solid, a liquid or a gas.

• Solid- Ice

• Liquid- Water

• Gas- Water vapor

Temperature Changes

• When temperature changes, water changes its form.

• This means there can be a change of state.• Liquid to a gas (evaporation)• Gas to a liquid (condensation)• Solid to liquid to gas (melting)• liquid to solid (freezing)• Gas to solid or solid to gas (sublimation)

Change of States

Evaporation

It takes energy or heat to move from a a liquid to a gas. You MUST add energy to the liquid for this to happen.

What happens in condensation?

What type of Energy is involved?

Changes of States

• Evaporation- the process by which a liquid changes into a gas. (Evaporation)

Evaporation

• Energy must be added for water to evaporate. – Cools the areas around. Think of sweating

and the body cooling.

• Sunlight or heat from the sun is our energy.

• Heat is a form of energy.– Kinetic Energy

It’s Hot Outside!!!

• On hot, sunny days evaporation of water off your skin can feel good.

• What about when humidity is very high?

Too much water in the air…

• When the humidity is very high evaporation cannot occur so the moisture remains on your skin.

Condensation

• Condensation is the process by which a gas, such as water vapor, changes into a liquid.

Condensation

• Energy is released when condensation occurs.

• This means that heat is given off by condensation.

Clouds form as a result of condensation.

-Describe the process.

Cloud Formation

1. Liquid water evaporates into the air as gas.

2. When the air containing the water rises and cools enough (dew point), water vapor will condense and become tiny liquid water molecules (requires condensation nuclei)

The Water Cycle

condensation

What is Dew?

• Water must condense on solid surfaces.(grass, cars, mirrors, etc.)-Dew is water that condenses on the ground because that surface is cooler than the air.

- What are these solid substances in the air called?

What about frost?

Humidity

• Remember, water is ALWAYS in the air.

• Humidity is the amount of water vapor in the air.

• Humidity varies with time and location.

Saturation

• When the humidity is 100% (cannot hold anymore moisture) the air is saturated.

• When the air is saturated evaporation = condensation.

Unsaturated Air

• If the humidity is less than 100% the air is unsaturated.

• Evaporation is greater than condensation.

Temperature is Important!

• How much moisture air can hold depends on temperature.

• Warmer air can hold more moisture than cooler air.

• Warm air has more Kinetic Energy therefore can hold more water. (air molecules are farther apart)

Cold Air vs. Warm Air

• Cold air is more dense so it doesn’t have as much room for water vapor as warm air does.

• This is why warm air can hold more moisture than cold air.

Relative Humidity

• Relative Humidity compares the amount of water vapor in the air to the amount of water vapor that the air can hold at that temperature.

• Relative Humidity = recorded as a percentage.

Example

• Air with 50% relative humidity (R.H.) contains half of the amount if moisture it can hold.

• Since R.H. depends upon temperature, you can change the R.H. by changing the temperature but not changing the water in the air.

Dew Point

• The dew point is the temperature at which air will reach saturation (hold as much water as possible).

• Comparing the dew point to the temperature of the air can give you an idea about the relative humidity.– The closer the two numbers the more humid

the air.