deposition

what is deposition

Deposition refers to the process in which a gas changes directly to a solid without going through the liquid state. For example, when warm moist air inside a house comes into contact with a freezing cold windowpane, water vapor in the air changes to tiny ice crystals. The ice crystals are deposited on the glass, often in beautiful patterns like the leaves on the window above. Be aware that deposition has a different meaning in Earth science than in chemistry. In Earth science, deposition refers to the dropping of sediments by wind or water, rather than to a change of state.

examples of deposition in nature

Deposition as a change of state often occurs in nature. For example, when warm moist air comes into contact with very cold surfacessuch as the ground or objects on the groundice crystals are deposited on them. These ice crystals are commonly called frost. Look at the dead leaf and blades of grass in the Figure 1.1. They are covered with frost. If you look closely, you can see the individual crystals of ice. You can watch a demonstration of frost forming on the side of a very cold can at the URL below. (Click on the mulitmedia choice Ice on a Can.). The ice in the can has been cooled to a very low temperature by adding salt to it. Q: In places with very cold winters, why might frost be more likely to form on the ground in the fall than in the winter? A: Frost forms when the air is warmer than the ground. This is more likely to be the case in the fall. In the winter, the air is likely to be as cold as the ground. Deposition also occurs high above the ground when water vapor in the air changes to ice crystals. In the atmosphere, the ice crystals are deposited on tiny dust particles. These ice crystals form clouds, generally cirrus clouds, which are thin and wispy. You can see cirrus clouds in the Figure 1.2. Q: Cirrus clouds form only at altitudes of 6 kilometers or higher above sea level. Do you know why? A: At this altitude, the atmosphere is always very cold. Unless the air is cold, water vapor will condense to form water droplets instead of ice crystals.

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textbook_image

instructional diagrams

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questions

conditions required for frost to form on the ground include

a) air that is warm and moist.

b) ground that is freezing cold.

c) ground that is warmer than air.

-->  d) two of the above

frost is most likely to form in winter than fall.

a. true

-->  b. false

states of matter involved in the process of deposition include

-->  a) solids.

b) plasmas.

c) liquids.

d) two of the above

the clouds in question 5 always form close to the ground.

a. true

-->  b. false

diagram questions

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