Evaporation and Condensation

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Part 1: Evaporation

Problem: What effects does evaporation have on the temperature of its surroundings?

Hypothesis: How do you think that evaporation will affect the temperature of the surface from which the liquid is evaporating?

Procedure:

Trial 1. Wipe an alcohol pad across the back of your hand and the hands of each person in the group. Report how your hand feels in your observations.

Trial 2. Repeat the above, but this time, blow across the surface of your hand. Report how this feels, especially in relation to the first trial, in your observations. Did the air passing over your hand in trial 2 increase or decrease the speed of evaporation?

Questions:

1. Does alcohol gain or lose energy when it evaporates?

2. Name two variables that affect the rate of evaporation.

3. In what way do winds affect evaporation of ocean water?

4. State two reasons why areas of water heat up more slowly than areas of land when both surfaces receive an equal amount of sunlight.

Part 2: Condensation

Problem: If humid air is cooled, how is the water vapor affected by the drop in temperature?

Hypothesis: If the air surrounding a beaker of water is cooled, what do you think will happen to the water vapor in the air?

Procedure:

Trial 1. Fill a beaker about halfway full of tap water and add some ice. Watch the outside of the beaker for changes occurring to the water vapor in the air surrounding the beaker. Record your observations.

Trial 2. Fill a beaker with water. Record the temperature. Add a moderate amount of ice to the beaker. Record the temperature of the water in the beaker when water vapor begins to condense on the outside of the beaker.

Questions:

1. What happens to a gas when it is cooled?

2. If the temperature at which the water begins to condense is called the dew point, what is the dew point in the classroom today?

3. If the air in the room was more humid, do you think that the dew point would be higher or lower?

4. As humid air rises and adiabatic cooling occurs, what may happen to the water vapor in the air?

5. If condensation is the true opposite of evaporation, how does condensation affect the temperature of the air from which the water is condensing?