The energy needed for the transformation is known as the heat of evaporation. How much energy you need depends on factors such as the type of liquid or the surrounding temperature. If it is already very hot outside, you will need less energy to vaporize a liquid; if it is very cold, you will need more. In order to turn into a gas the molecules held together inside the liquid have to break free to get into the air.
This means the hydrogen bonds holding the molecules together need to be broken. Thus, molecules that are able to form lots of hydrogen bonds among themselves are much harder to turn into a gas and have a higher heat of evaporation. This also affects the boiling temperature of a liquid.
Molecules that attract one another very strongly start to boil at higher temperatures compared with those that have weak attractions. A lower boiling point generally means a liquid will evaporate more quickly.
Water, for example, with one oxygen and two hydrogen atoms, can form two hydrogen bonds per molecule. Its heat of evaporation is 2, joules per gram, or calories per gram, and it starts boiling at degrees Celsius degrees Fahrenheit.
Your body makes use of the evaporative process when sweating. Sweat, which consists of 90 percent water, starts to evaporate.
The necessary heat of evaporation is extracted from the sweat itself, which leads to a heat transfer from the liquid into the gaseous state. This results in a cooling effect called evaporative cooling that helps to maintain body temperature and cools the body down when it gets too hot. The degree of cooling is dependent on the evaporation rate and heat of evaporation. In this activity you will find out which liquid has a greater cooling power: rubbing alcohol or water. What do you think will cool more when it evaporates?
Observations and results Did you feel the cooling power of water and rubbing alcohol? Both liquids should feel cold on your skin. Blowing on your wet hand helps the water and alcohol to evaporate.
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Evaporation and Climate In order to understand why growing food uses so much water, we need to explore the process of evaporation.
Water evaporates faster when the air is dry. When the air is dry, there are fewer water molecules in the air returning to the liquid, so the water evaporates faster.
When the air has many water molecules in it i. Try this investigation: Put an equal amount of water in three identical jars. Leave one uncovered, cover another one with aluminum foil, and cover the last jar with a tightly fitting lid Figure 5. The tighter the lid, the less evaporation. But why, exactly? Students might suggest that, with the lid on a jar, the water molecules have no place to go.
Surface area. Increasing surface area will provide more surface from which water can evaporate. To summarize, evaporation is slower, occurs only from the surface of the liquid, does not produce bubbles, and leads to cooling. Boiling is faster, can occur throughout the liquid, produces lots of bubbles, and does not result in cooling.
In its simplest form, the water cycle is how water changes from being water vapor a gas to liquid water condensation and then back to a gas evaporation.
Holy cow, it just hit me how many real-life applications we found for this one simple topic. Contact him at: DrMatt msb-science. Labs Physical Science Elementary. FIGURE 4 Wind causes the water on your skin to evaporate faster, which takes heat away from your skin faster, making you colder.
These changes between states melting, freezing, and evaporating happen because as the temperature either increases or decreases, the molecules in a substance begin to speed up or slow down. In a solid, the molecules are tightly packed and only vibrate against each other.
In a liquid, the molecules move freely, but stay close together. In a gas, they move around wildly and have a great deal of space between them. In the water cycle, evaporation occurs when sunlight warms the surface of the water.
The heat from the sun makes the water molecules move faster and faster, until they move so fast they escape as a gas. Once evaporated, a molecule of water vapor spends about ten days in the air. As water vapor rises higher in the atmosphere, it begins to cool back down. When it is cool enough, the water vapor condenses and returns to liquid water. These water droplets eventually gather to form clouds and precipitation. Evaporation from the oceans is vital to the production of fresh water.
When that water evaporates, the salt is left behind. The fresh-water vapor then condenses into clouds, many of which drift over land. Precipitation from those clouds fills lakes, rivers, and streams with fresh water. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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