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Chapter 2, Lesson 3 Multimedia

Condensation Cup

Very cold water is placed into two plastic cups. One cup is then carefully placed in a ziploc bag and sealed tightly. The other is left exposed to the air. After several minutes, the cup left exposed to the air has condensation on it, while the cup in the bag does not.

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  • When a cup filled with cold water is exposed to air, the water in the air condenses onto the side of the cup.
  • If the cup of cold water is not exposed to air, no condensation will form.

Condensation

This animation shows water molecules, represented for simplicity as spheres, condensing on the side of a plastic cup.

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The fast-moving molecules of water vapor transfer their energy to the side of the cup which is cooler. This causes the water vapor molecules to slow down. When they slow down enough, their attractions overcome their speed and they stay together as liquid water.

Water Cycle

The water cycle as it occurs in nature.  Water falls as liquid in the form of rain, evaporates from the ocean, and moves through land via runoff, aquifers, and groundwater flow.
  • Energy from the sun speeds evaporation of water from the ocean and from water on the land.
  • Cooler temperatures in the upper atmosphere cause water vapor to condense to tiny droplets which form clouds.
  • When the clouds become saturated, it rains and the cycle continues.

Evaporation and Condensation

This animation shows space-filling models of water molecules in a liquid, then moves up to the surface to show some water molecules evaporating, while others condense into the liquid.

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  • Water molecules break away the surface of the water (evaporate) and also rejoin the water (condense).
  • In a closed jar or terrarium, the rate of evaporation and condensation would eventually become equal. This video appears courtesy of Roy Tasker.
    © Roy Tasker, VisChem Project.