Chapter 12 Section 1 Where does water in the atmosphere come from? Objective: Explain how water gets into the atmosphere

Key Terms evaporation: changing of a liquid to a gas transpiration: process by which plants give off water vapor into the air

Water Vapor Water in the air is in the form of a gas called water vapor. Water vapor is an odorless, colorless gas. Water changes state at ordinary temperatures and pressures. Water leaves the ocean as a gas and returns as a liquid.

Water Vapor Water is found in the atmosphere as clouds and fog. These are made up of tiny droplets of water or ice. It has been estimated that there are a total of about 14 million tons of water vapor in the atmosphere.

NAME: What is water called when it is a gas?

Evaporation Evaporation: the changing of a liquid to a gas This is how water vapor enters the air. Most water in the air evaporates from the ocean. Water also evaporates from lakes, rivers, puddles, and wet soil. Winds carry the water vapor in the air all over Earth’s surface.

2. IDENTIFY: Where does most of the water in the air come from?

Heat and Evaporation When a liquid is heated, its molecules move faster. Evaporation occurs more rapidly in warm liquids Evaporation from the oceans occurs most rapidly around the equator, where the water is heated by the more direct rays of the Sun

3. DESCRIBE: What causes a liquid to evaporate faster?

Living Things and Water Vapor Breathing adds moisture to air. Plants also give off water vapor through a process called transpiration. Occurs in the leaves of plants through tiny opening called stomata.

4. NAME: How do plants give off water vapor?

12-1 Classwork About how much water vapor is in the air? How do animals add water to the air? What happens to the molecules in a liquid when they are heated? What part of a plant gives off water vapor through openings called stomata? What is the gaseous form of water called?

12-1 Classwork continued 6. IDENTIFY: Where does most of the moisture in the air come from? 7. HYPOTHESIZE: If you wipe a damp cloth across a tabletop, the table is wet. What will probably happen to the water in a few minutes? Why?